John,
Here's my solution. It's a Monaco Dynasty with 8.3 Liter Cummins and a United Expressline 24' Racers Special.
This gives us plenty of living space as well as the necessary space for the car, tools, spares, and working area.
The trailer is rated for 10K GVW. I wired it for AC and can run everything, including the compressor, from the diesel generator in the coach.
The coach also has much larger water and holding tanks, as well as greater carrying capacity than you're likely to find in a toy trailer. It also drives much better and you have access to the facilities while on the road.
Later,