Thanks, Pete. We decided to add the pipe insulation to the garage. Hopefully that will give it some extra life.
OK, folks. I still can't get a design that meets all my criteria so I decided I was asking too much. In the interest of aerodynamics I've ditched the more traditional cargo trailer loading idea. Told BF we won't be loading the motorcycle into the camper. Here's the current design I'm leaning toward:

It's too large to be a tiny travel trailer but it's not too huge. Overall length, including trailer tongue, is 15'. It should be about 7.5' tall. The camper section is 12' L x 6.5' W. We can get the recumbent trike, folding bike, folding kayaks & dog gear into it while still leaving room for us to all pile in & sleep without unloading anything or rearranging much gear. That's an imperative since we always get to campsites late, usually right as campgrounds are closing for the night. The next day we can unload & set up camp proper.
There's room for a tiny galley-like space in the rear though it's meant as food & kitchen storage, no cooking in there. I figure the kitchen will be set up behind the trailer. Most of the space under the bed is pass thru storage where the trike can ride, leaving the forward area for more weighty items. If we're not taking much gear then we can load the trike in the front area instead. Under the bed & between the wheel wells will be space for lightweight storage, like clothes, toiletries, etc. We can fit table & chairs inside if the weather were bad enough. Some gear will go in the box on the tongue. Where things get loaded will depend on what we are carrying.
Have debated the idea of a drop floor just forward of the wheels. I know BF would appreciate the headroom. There's only a small area where he can stand up straight. (The max interior height is 70".) He'll need to duck to get through the doorway. Decided that I really don't want to do that kind of building. My attitude is that I'm building it so he can just deal with it.

If we end up doing so much camping that the lack of headroom inside really bothers him then somewhere down the road we can discuss putting in a drop floor. Am I being mean?