The trailer will be perhaps the one variable which will change without much control. :P This is what I call an "opportunistic tow vehicle" - it's designed for pulling things, that pop up in availability, being an incredible deal if you have the cash to get it, if you are looking for... whatever that happens to be. It just so happens there's a very large shopping list as this would be the main fetch vehicle for an intentional community that would like everything from someone's decommissioned ham radio antenna (I saw an antenna rig free for the taking that must've cost $6000 new on craigslist once) to decorative tile to free firewood to an inexpensive travel trailer to be someone's temporary housing.
The main tow trailer I hope to get/build/modify to basically be a flatbed with a low profile (low as the car/truck) with aeromodding to most often tow things like 2.5 cords of wood at a time, move a skidsteer or utility tractor/old farm tractor around, be able to move a wrecked car/pickup around, haul alot of scrap wood at once, move 5 tons of brick at a time, etc. It's kind of a nice size between the 3500lb small trailer level, and the truly large Class 6/7/8 type stuff, the max legal weight you can move without a CDL, probably the max weight most people would ever dare attempt without more specialized training and similar. Over this weight the trailers get so damn heavy and the loads would be rare I would think.
Although I was exploring the possibility of hotshotting a dozen empty sealand containers on a 40ft flatbed somewhere or school bus shells stripped of engine there are few loads over 10k which seem to justify a customized tow rig to haul them. There's also not any SVO suitable engines for moving well over 10k without going up to larger trucks and that by itself is the majority of the potential savings here. Something that can pull 10k efficiently off almost free fuel I believe would pay for itself even though it's only it's part time infrequent job. Saving $500 or more per load of fuel, trailer rental fees and vehicle rental fees (let alone hiring a driver) adds up pretty quick is my logic. Many jobs can be done by the 3500lb class trailer but some just flat out cant like moving a skid steer around, one which only needs to be moved a handful of times anyways. No one job makes it pay for itself, it's a number of smaller jobs that are all solved by this one 7-10k class vehicle which if you can DIY solve everything, especially if the vehicle is SVO fueled and a separate project for low cost plant oils works out. (the vehicle is planned now but may not be built unless the plant oils are able to be produced cheaply - if they are not it just takes 3x longer to pay for itself so it needs more careful analysis to really work well)
Other trailers would include eventually a heavy car/pickup dolly suitable for moving 4x4 1 tons around at the stouter end of the scale. But also things like a travel trailer to pull one way to a destination are on the table - a great deal on one wouldn't be turned away I mean, so it's not exclusively about one trailer. It would probably be used with the 3500lb rated single axle trailer for lighter loads as well.
By 10k travel trailer you dont mean 10,000lbs behind a Charger..?? People were heckling the crap out of me for considering 7000lbs behind an even larger Caprice. Thats why I finally crapcanned it and changed to a pickup framed idea.
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To aerohead: whether car or pickup body adding 1 foot to the nose, and 3 feet to the tail not a problem. Hope to couple the aero of the tow rig to trailers as well insofar as possible, and aeromod the trailer rears to boot. May well aeromod individual loads on a flatbed like some kind of temporary boattail on the utility tractor... all depends how cheaply such things can be done on the quick since they either have to work for multiple objects being pulled or be cheap enough to be disposible. If reinforced cardboaard boattails would work that might solve the cheapness problem but I don't think it'd take the load even at just 55mph.
And btw your pickup is actually my inspiration.
I've seen your pic around before. My main question is would I be even better off starting with a Caprice sedan/wagon body due to lower overall profile, steeper windshield rake and similar? Or do you think, with the same above mods that a pickup probably be about as good as the car? (the pickup actually preferred if possible - such a twist may even allow a fifth wheel or gooseneck) Do you think the starting pickup body is likely to make a huge design? I don't know how much of the Ford F150 lightning is due to the center section being aero or due to other things (lowering, skirts), but it seems better than the horribly unaero dodge rams. But maybe even those, with the 1 foot nose extension and 3 foot boattail would turn out similar numbers, i've no clue... thats what i'm trying to narrow down, what vehicle body to START with.
Oil_pan - I know, thats why a diesel would be swapped into there unless it was one that came with one in there. And note my wacky idea for a 0.50:1 shiftable overdrive with a reversed NP203 rangebox so it wouldn't matter if they only came with a 4.10 or worse, even if I used a TH400 or 1:1 stickshift on there. Low gear is needed to get 10k weight moving, yet unladen tolerable cruise rpm's are obtainable with the range box. Alternately i'd explore the use of late 70's full size passenger car 12 bolt rear ends with 2-series axles, and use the NP203 rangebox as an underdrive. Even if the axles are not exceptionally strong and don't last under 10k towing they are so cheap and unwanted in wrecking yards I could bring home half a dozen. Cheapness of replacement parts is as much a part of the design as other things, since you have to build off used parts, but the odds are in favor that even if one is bad they all wont be bad.
Aardvarcus - hmm, I wasn't aware of that. I'll have to research it a bit more. I'd never heard they could stick 10k in the back, are you sure on that figure? Can it run off SVO is a critical question though, I expected to need IDI to run it because that's 2/3 of the financial savings right there. It may still get built without SVO fueling but planning for it there is important right now. I'm also curious what kind of mpg (the 30 unladen i hope to exceed?) and reliability I could expect from such a vehicle, within my budget I plan to pretty much have rebuilt the engine for instance (GM 6.2's have been available as crate engines for a little over $2k for awhile, a rebuild should cost even less) and if it ever craps out replacements are not unobtainably expensive. The same reason i'd be leery to buy a big semi to haul other loads (if it craps out I can't afford to fix it, cant afford to rebuild it, have to run it til it breaks) make me less enthusiastic about some of the other medium truck diesels.
I mean case in point schoolbusses are commonly available for under $2000 - I could aero one and they handle the weight, but I wont be hitting 30mpg with one towing 7k. Ever. Yet a diesel converted Cadillac Fleetwood is rated for the weight and should hit 30mpg unladen. I'm just realizing that I really do need more than 7k once tare weight of all available trailers is taken into account. The skid steers I might want to move around probably 5500lbs plus some implements. 7k is just not enough towing ability, I have to take risks and compromise safety stretching above a limit that many consider marginal in stock form despite our normally paranoid US tow ratings. If I could move 8500lbs without raising hackles i'd still do a sedan though. FWIW my proposed 'bulk material tow' vehicle for getting over 10k would be a schoolbus with 10k on it's back and another 10k in a trailer behind it both aeromodded. There are no single item objects that need more than 10k in weight, just huge masses of firewood, brick, scrap metal and whatever. That's also legal without a CDL. It just needs enough gear and power to move the load.