The conventional fifth-wheel RV trailers have this same situation, although the current trend (especially for larger units) is the "high profile" design, with full standing headroom around the bed, so the occupants of the bed are not so close to the ceiling.
They generally have a roof vent (just like ours) in the bedroom, often powered; a second air conditioner is often available for that location. I suppose someone could mount an A/C unit on the front of a Scamp
19', but I don't know that I would want to be that close to one of those noisy things.
In addition, they usually have ducted air conditioners, so cool air is directed to all areas of the trailer. There is no roof truss space in our eggs to accommodate the A/C duct, as there is in a stick-built trailer, but it seems from Nita's post that someone has found a way to get close.