I know this is a more complicated solution, but have you though about a longer MH that has a garage as part of the RV box portion? Then get a two-car tag trailer to replace your three-car gooseneck trailer. Once at your location, the vehicle in the garage stays outside and you can use the garage for sleeping area. Lot of toy haulers use fold-down bunks, you could do similar or just an air mattress.
I've actually been giving your suggestion a bit more thought and the more i think about it, the more i like the idea. Enough so that i think this is the route that I'd prefer to go for several reasons really.
One, this would give me more sleeping space as you mentioned. Two, by fitting one rig inside the garage, that will allow me to use a shorter trailer (thinking max of 32' tag trailer) which should put me closer to being at the length limit. Three, if i want to just take a trip wheeling by myself, i don't have to haul a trailer at all. There were a couple other reasons i like this better but as i sit her in front of the keyboard...I'm drawing a blank. go figure. lol
The one question that i do have about the Toters with garages; what are the dimensions of most garages? I know that is a hard question to answer, but I've seen a few that are 16' long which is great, but my concern is the dimensions of the door. The rig that will be going into the garage is 92" wide, 80" tall, and just under 15' long.
I do have a set of smaller rollers that i could throw on the truck to fit it within the width of the garage opening, but that'll be a bit of a pain to swap out each time i go play. On hindsight, that's not much of a difference than what i had to deal with when i had my diesel drag truck. lol
Another question for those "in the know", any idea why someone would have a Toter build with a garage but not put a rear entry door to drive a vehicle inside? I recently found one out in SC that looks beautiful and like it would work, but there is no way to get a vehicle inside short of cutting the back wall off and building a door myself.