There is a thriving 'teardrop' trailer industry right now with all these people looking for tiny homes and whatnot.
I forget the brand but there is one that comes with an optional room AC in the front wall. Others have the traditional rooftop AC like RVs have.
Than they have a trap door in the back to open up onto a kitchen. All sorts of tiny things inside these things these days. Including forced air electrical heaters if you'll be RV Park camping, or propane if not and you plan on some cold weather camping.
So maybe search for teardrop trailers?