You could stop and charge periodically...but for those of us with jobs and using our limited free time to go somewhere or do something with the kids, you may not be ready to stop and do something else beside drive while ou wait for the batteries to be charged. Yes, I agree that we should be willing to make certain lifestyle adjustments for the planet, but taking a 3-hr break in the middle of a trip might be asking more sacrifice than most folks are willing to put up with in order to drive an EV...especiall when by making the trailer powerful enough to eliminate that break, you can do your trip and git 'r dun....then unhook the trailer and go back to being a meek and mild little plug-in EV. I see it as giving an EV a dual personality...something that can lightfoot it around town while still retaining the highway range of a standard ICE car.
Yes, it would be a mobile charging station....with enough output to help the car over those hills or while carrying a load such as us, 2 teenagers, camping gear, and a couple of bicycles. I would want it to put out enough power to drive the vehicle on it's own at a reasonable speed (55 MPH perhaps?) on flat ground even if the batteries were dead, and to climb a hill with a good charge. I would have no problem shifting to first to make it up a hill as long as I could at least keep up with the semi-trucks and their loads.
Of course the original concept was to reuse components off of the original donor vehicles....you know, the whole reduce, reuse, recycle thing rather than buying more new/used stuff. Hence the ICE from the car, driving the big electric motor from the forklift as a generator with the other smaller 2 motors being used to move the car.
So far, I have yet to hear why reducing the duty cycle of the ICE/electric combo to meet reduced overall need is not a good idea; why not just run it only when the voltage falls below a certain level then turn it off again? Of course it might run continuously while climbing a mountain pass but that is why it is there....it'll stay off most of the way down the other side! Your comment about weight being the main reason I've heard to go with a smaller engine. Yes, weight may be an issue when using a diesel engine as the ICE....I'm not sure what's going to weigh less, as I just found some of these smaller diesels and have yet to look them up, but I suspect that a small automotive diesel might be fairly light compared to a similar-sized industrial diesel (see
2815 - Diesel Engines & Components at Government Liquidation )and probably cheaper too....perhaps this may be just one of the compromises to make to make an in-town EV highway-worthy without breaking the budget. Considering how little time most cars will spend on the open road compared to pulling daily commuting duty, some tradeoffs might be worth it. Of course, perhaps the ultimate answer may be to top looking at diesel for this application and we may have to look at that option at some point.
Camping storage is a minor factor...we often backpack, canoe, and bicycle-camp, so we can pack pretty tightly and we don't "take it all" with us. At any rate, if this trailer is also designed as an aerodynamic boattail, storage space should be available in the fairing...and we don't take our microwave, hair dryer, and easy chair with us, so I don't see much weight for camping gear..maybe 100 lbs at the most for 2-4 people.
If taking a road trip in an EV was as simple as strapping your Briggs and Stratton gen-set to the trunk-lid, why aren't more EVers doing it?