My take:
1: Automotive grade locks (I'm talking the Strattec/BOLT type) on the doors and compartments. Winnebago does this. Having only one key for the entire RV is nice.
2: TPO/EPDM roofs just need to go. Instead, something like spray on epoxy elastomer coatings like rvroof.com or Rhino Lining should be used. This way, there are no issues with caulk or seams.
3: Ditch fiberglass insulation, go with something more modern, rot-resistant, environmentally friendly, and critter-unfriendly. Rock wool comes to mind, so does Styrofoam and Thinsulate-based insulation.
4: Toss the antediluvian furnaces and water heaters. Instead, use Alde or Truma units which can do the function of both devices, far more economically.
5: Keep the spare tire, and include a usable jack for it. Fix-A-Flat cans don't count.
6: Solar panels on the roof, a decent charge controller, a beefier battery bank (400 amp-hours or so), then toss the absorption fridge for a compressor fridge. This gets rid of out-of-level issues, fewer holes needed for vents, and actually gets the beer cooler to boot. Because a compressor fridge uses 3-5 amps, having at least 250-500 watts of solar and a battery bank of similar capacity will help with allowing the fridge to run for long periods of time. Solar is always useful in any case, so if a rig can support solar panels, it should have them, combined with a MPPT controller (since every watt is precious.) Plus, if the solar panels are mounted on a frame (not glued on), they actually provide "shade" due to a layer of air between the panels and the rig.
7: If the motorhome is a diesel, stop with the LP gas generators, and put diesel generators in. For vans, Onan models may be too tall, but PowerTech makes a model that I've personally seen installed under a Sprinter, and it did not extend down past the axle, and was not in the way of the angle of departure. LP gas generators just are too thirsty to be useful, especially in climates like Texas where A/C use is a must.
8: Some type of strongbox for laptops and such. Custom metal fab work for a strongbox that can fit in a wheel well or other nook isn't that hard to do. The lock doesn't need to protect Fort Knox -- something like a Simplex LD-450 or a Simplex 960 would be good enough, perhaps with the option for an actual safe lock if people actually want that... however, the strongbox is more intended to keep a laptop from walking off, as opposed to TL60x6 duty. Bonus points if the strongbox can allow charging of devices though a hole.
9: Most class "C"s have a blank wall on the back, or perhaps a ladder. It would probably take some engineering, especially reinforcing the wall for the heavy loads, but it would be nice to have some type of fold-out shelving on the back. This would be quite useful for carrying spare fuel cans, water jugs, a bicycle or two, or just a spot for mounting the spare tire so it is accessible, but yet out of the way.
10: Have a generator controller built in, like the Onan EC-30. This way, one can set it so if the house batteries of the RV are low, the rig can fire up the generator for a few hours if the charge gets below, say 60% SoC.
