Some have mounted a window AC unit sitting on the back bumper and coming through the wall under the table. As I recall the advantage of having one with a remote control was mentioned.
Older Scamps did have window AC units as stock AC. In bottom of closet or I think in Cabinet on some years. Nice part is the price is way cheaper than an RV unit and replacements are available everywhere.
Myself I would be nervous about a unit in a window. However there are many threads about people doing just that. Some by building supports from tongue or rear bumper. Along with some having beefed up what they replaced the window with.
There is plywood attached to the back wall of my scamp under the liner and I think this is common. For tire and table mounting hardware the plywood gives material for bolts/screws and spreads the weight
out so fiberglass can handle the load without cracking. It would I assume also help that back window area support the weight of a tiny window AC unit and the smallest they commonly sell would I'm pretty sure be sufficient for a 13 ft. or even possibly a 16 ft. depending on climate and sun exposure.
RV models are way over powered for a 13 ft. scamp or even a 16 ft. Most of the AC units used in RV's are all the same size and you can see pretty large RV's with a single unit.
It can work because folks do it but it isn't a trivial modification in many cases. Not super difficult but not trivial. Also not all older scamps have the roof bracing for an AC on the roof. At some point it became standard to include it but as I mentioned through wall was common design and roof mounted was at least at one point a special order so the support and power are not there.
Heck mine didn't have a battery
box since back then a house battery
was an "option". It also doesn't have the framing for a roof mount AC.