Some more info:
We are looking at a Grand Design Momentum 399TH.
It supposedly has a 13' garage. But I think some of that is taken up by the rear doors/screen.
So I figure about 12'6".
I also figured the width conservative due to various things like protrusions from the walls that may be an issue.
So 94" is what I settled on.
(Obviously measuring a 399TH would be best. But we haven't been able to find one to measure yet.)
We then taped this off in our driveway and did a test fit. It appeared workable. One thing about the diagonal measurements...
People are assuming the quads are rectangle shaped when viewed from above. The Arctic Cats are not. The corners are slanted or cut off. This makes a diagonal calculation based on overall length and width inaccurate.
We presently load them on a 96" wide truck bed rack side by side.
It is a very tight fit.