Mike,
I haven't made a final decision on the clerestory wall in the rear. It will either pivot down and rest in a channel with drain holes on each side of the trailer, or the clerestory wall will be fixed along with the rest of the upper section. The channel and drain holes would then be located at the height of the bottom of the clearstory wall, when the pop-up is stowed.
Hinging the clerestory wall at the top would be the easiest, but....
As far as raising and lowering the pop-up, I've been looking around on the internet at those heavy-duty drawer guides, which would be used to give me the tracking system. I haven't found what I'm looking for, so I'll probably end up building those as well. As far as providing lift and descent for the pop-up, I haven't made a comitment on that as well. The only system I have seen for that, is Sumner's cable system. I do have a friend that is quite the machinest and maybe he could machine some screw jacks for me. (I don't like the idea of a chain skipping a tooth on one sproket, of multiple jacks) There's some more food for thought at bedtime!
As far as weatherproofing goes, the roofline at the top of the clerestory wall, will be extendened a bit, so when the pop-up is stowed, the extended lip on the roofline will conform to the body, just in front of the galley hatch hinge and it will compress against a rubber boot at that location. I may end up hiding the galley hinge under the lip as well. (But I don't like the idea of only being able to get into the kitchen when the pop-up is raised)
When the pop-up is raised, my only concern about water, is at the base of the clerestory wall and I believe, That's one's a gimmie. I will need to address the perimeter with some sort of weatherstripping, so water can't be forced upwards in between the pop-up and lower exterior walls, in both positions.
Speaking of boatbuilding, I'll probably end up doing the body sides with wood strips on the exterior and use either aluminum or stainless steel ($ Ouch!) on the roofline.
Hey, this is just a drawing right now. I haven't ruled out the possibility of nixing the pop-up and learning to crawl again.
There is still much consideration at hand, before I start building. I was reading a post last night about the guy who was having a heck of a problem with condensation. Hmmmm.
The only thing that I'm comitted to right now is going with the extra length, so I can have a killer galley and not get crowded out elsewhere.
It's the extra length that's got me pondering things about designs.