I converted a 28' gooseneck into a toy hauler. Mine is +1' height and has a full 8' door with 5,200 lb axles. It is not as nice as some factory built toy haulers but works well for me. I have a California king mattress over the goose which sleeps much better than a "camper mattress". The kids sleep on two oversized camp cots once I pull the rig out. I added fresh water tank, cabinets, a sink, hot water heater, and a bathroom with shower and chemical toilet. I opted to go this route instead of mounting permanent black and gray holding tanks. Since the toilet is self contained, I just use a portable tank for gray water for the sink and shower.
I used VCT commercial tile in the floor with aluminum tread plate runners where my tires drive in. It already had an AC unit on the roof with heat strips but I also run a 2 brick ventless propane heater if very cold. I pulled the inside paneling off and added 1" styrofoam insulation in the walls and recovered with beadboard. I also added an RV awning on the side which has been very nice for shade and rain protection.
If I was ordering a new one, I would insulated walls from the factory, get a standard RV width walk through door with screen, ac unit, powered roof vent fan, and breaker box wired for 12 and 120 volt.
