All of these suggestions should not add to the length or much to the weight of a particular model trailer:
1. A stout sewer hose bumper. Why manfacturers are going with those flimsy plastic rear "protusions" is anybodies guess.....what are they thinking ??? The bumper is a perfect place to store the sewer hoses, and if stout enough to carry the spare tire instead of sticking that under the tongue or elsewhere. We have a sewer hose bumper.
2. Compartment doors that are as big as the compartment. To many times I see huge storage compartments that have tiny doors. Thank goodness we have the big doors.
3. Water heater as near the faucets as possible. A water heater stuck at the opposite end of a trailer causes a lot of wasted water. I will sometimes capture the cold water to flush my toilet. In our camper, I don't see many other placement possibilities, so I know that request is an engineering nightmare.
4. Slides that do not impinge on the use of the camper in the closed position.....that is a biggie for us. Too many times, you can't get to the fridge or bathroom, or you gotta squeeze by the slide to get to something. I went to a dealer in PA. to look at a particular model that we thought would fit our needs before we bought our current camper. Looked great with the slide out, but when I asked the guy to close the slide, that camper was no longer on our list.....that puppy took up a lot of room. 1 reason we love our camper is that we only loose 2 small cabinets with the slide in, and everything else is usable.....and we do.
5. The dinette and sofa should be across from each other instead of side by side. We have entertained up to 7 people in our small camper, and everyone can face everyone else without excess turning in their seats. I can't imagine how you can do that when the sofa and dinette are side by side.
I know I can only suggest 5 items, but torsion axles over the spring and shackle setup is a big plus.