Probably more appropriate for the expensive "camping" trailers...even a small one of those costs like $25K...all the way up to big ones that cost well over $100k. Airstream prices are serious!
Also, probably doesn't need a big battery pack or powerful motors. You're right that a big battery for range would be a waste in most rarely-used trailers. But, with a small battery more like a hybrid car setup, the trailer could provide some boost for accelerating, support on hill climbs, and some regen braking. A Chevy Volt type battery pack was only like 15 kWh, but that chemistry could charge and regen at high power.
Add some solar on the trailer roof, and you could use the battery like a Powerwall and get rid of the gas generator while parked/camping too.