So sometimes you get lucky, and other times you get REALLY lucky.
I did a little research last night, and there's a unit made by Frigidaire that evidently misses the "Energy Star" seer rating by .1 points, so since it doesn't make the mark, it sells for WAY cheaper than Energy Star units (even though, for all intents and purposes it actually is
Energy Star compliant). The unit is also only 15 amp (vs. 20), so it's not a lot of strain on a less than stellar electrical source. Several of the reviews I saw mention running the a/c easily with a Honda generator. Not only that, but the ratings on Amazon, Lowe's, etc. are almost all 4 or 5 stars.
It's $129 at Lowe's, so it was fairly painless to just go pick one up today. It's made for 150 sq. ft. rooms, which is about perfect for my 25' Airstream (now that I've installed all the polyisocyanurate rigid panel insulation and sealed everything up with foil tape).
But here's the kicker... the A/C is EXACTLY
the same size as the hole that already exists in the side of my Airstream for the old water heater access. I mean, I doubt it would be any more perfect had I cut the hole to size just FOR the a/c. There's about 1/8" clearance on each side (or less), and a little less than an inch on top (which is actually great to let it tilt down a bit to allow condensation or rain water to run off the back instead of into the Airstream).
I plan on doing some bracing around the hole to make things a little more polished and solid, but even just setting the a/c in place without any preparation is pretty satisfactory! Score.
I'll obviously pull the unit in during travel, but once we get there it just slides into place and locks down with some clamps! Not a bad solution for "meanwhile" as we're finishing the restoration but still using the AS. I may even end up making this a more permanent solution if it turns out the unit works well in cooling the AS. I would probably create some kind of drawer-rail type system to make sliding the a/c in and out easier, and then just fabricate a hatch that can lock closed.
The size difference between the new window unit and the old rooftop unit in the photo above is pretty hilarious, especially if the little thing ends up working well.