Christ is right, there's a ton of extra weight in there. Consider revising how things are packed in the cupboards so that a simple velcro strap would hold it all in instead of a wooden door. My parents motorhome had mirrors, on the walls and cupboard doors. Excess! In fact, all the cupboards and closets are solid wood, I'm sure there's over 500lbs if not more. At least 100lbs in mirror glass I'm positive of.
Does the fresh water tank need to be so big, or can you make do with a smaller one? All P-tex piping, nice lightweight, not heavy metal or semi-heavy pvc? Maybe not cost effective to change that, unless you get a deal.
I honestly can't think of much else I'd skimp on, as a good sized grey/black water system in necessary, seat cushions, mattress, quite comfortable when sleeping. Ditch the TV system if there is one.
No microwave or fridge or stove etc? A portable coleman stove and a 30lb LPG tank is far lighter than the massive drop-in stove/oven system my parents coach has. Microwave is cool, but we only used it to reheat what the freezer kept cold. Counter productive, eh? I suppose when in remote places it makes sense, (which is where my parents use it the most). Simple planning makes a fridge and microwave useless. I saw 90% of the western US national parks in a suburban with an ice chest. Planning indeed.
One sink, not two. Kitchen only, no bathroom sink. If you have two, save some plumbing weight, and open up some counter space! Or use it like a bowl, seal the bottom.
I wouldn't ditch the AC, but rather find a way to make it more streamlined, or sunk into the coach more. Coaches don't have great interior air circulation, so cooling the interior off when its baked may prove difficult. If you get a few solar panels up top, maybe have those run the coach AC system? Not sure on power requirements, but that's fairly easy to work out. Or even just gutting it so its just air circulation, no AC. That'd be simple, like the popup vent you suggested. A big fan to suck the air out, like attic fans for houses.
Certainly swap all the interior lights to LED, that'll save the battery and alternator.
Sorry if this post seems long, but my parents took us kids across the nation several times, so I'm fairly familiar with the truck vs. motorhome camping.
Oddly enough my parents have moved on to the truck towing, so a 32' recreational trailer (back 13' is open for bikes or snowmachines) is the new toy. That sucker weighs over 7000lbs dry! Granted it has extra insulation for those cold Alaska winters, but it and the truck push 14K lbs, which is heavy! Too bad no one makes a rec motorhome that'll combine the two.
Well I'm outa time, leaving work now. That's all I could think of! Hopefully some of it makes sense and is useful.
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