I've been going around and around on this very subject, and I finally found something that works - 28' Carson Fun Runner, bought it used at a local RV dealership. MOST of the toyhauler "garage" spaces I found were in the 11.x-12.5' range (I found none big enough with a wall separating garage from living quarters, at least in a size I was even remotely interested in).
This one's "garage" area - from back door to the cabinet on the left - is about 14'. The car fits comfortably - maybe 6" to the back door, a foot or so from the front bumper to the cabinet.
It is a hassle to load; the deck is pretty high. I have to put the rear wheels of the truck on ramps, and the door/ramp sits on wooden ramps made out of 2x10s. The clam ALMOST drags before the front wheels get on the ramp, and the first time it went into the trailer, the car bottomed out right at the jacking point/middle of the car (the two rivets dragged). That was before I had the truck on ramps - once the truck was on ramps, it went out/in without issue or drama.
Car is stock height. In the pictures, yes, I know that the right side strap is too small, yes, I know that the car is offset to the right, it was a "mock" load.
Once strapped in (even with straps I'd not actually use), neutral/parking brake on/rubber chocks behind rear/in front of front wheels, the car does NOT move. Pretty happy with it.
GVWR for the trailer is 12k# or so, it weighs ~6200 empty, fresh water tank is currently full, so it is about 7000# right now - add the car, it is OK. Tows fine. Still plenty of room in the "kitchen."
It took me a while to find it, plan on using the trailer for snowmobiles/skiing in the winter, but finally, I have ONE trailer for both stupid hobbies.