Thanks for your comments jandmz. I'll have to think about eliminating the bathroom sink... that might be hard to get used to, ha!
I have to confess -- and this is a from a no-experience trailer traveler -- I'm real paranoid about putting holes in the roof. I've nixed skylight/vents, too, though they can provide some lovely ambient lighting that would be especially useful if I decide to go with the darker earth-tones inside. But pretty much everything is still on the table, to one degree or another, while I'm designing.
What I've tentatively decided on is putting a small window AC under the front couch/bunk near the curbside wall, and running some kind of (probably rigid foam) ducting to the side (the red outline in the illustration), with a grille over it. (I've found 5,000 BTUs with dimensions of approximately 16 x 16 inches, 12 inches tall). This would prevent outside access to the area under the seat, unless a cargo hatch were positioned streetside. But then, it could always be accessed from inside. Since there won't be any propane tanks, I'm planning a box on the tongue for things like shore power cable, water line, etc.

Anybody see anything objectionable about this location and ducting for the AC? The only thing that occurs to me is that it's near the floor and cold air sinks... so it's putting cold air where the cold air has already settled. But geepers, the whole space is less than 600 cubic feet, so how big a problem can that be?