When I had an RV shelter built, we owned a 24' WGO View so I spec'd 30ftx12ftx13ft. Our new WGO Vista barely fits. It's a PITA to open the exterior bay doors and the A/C clears by ~4". The mirrors clear by ~4" on each side. When I park it dead center, a support beam blocks the door from opening completely. If I could take a Mulligan, I'd have gone with 35x14x15. But, as they say, "IF a frog could jump, it wouldn't bump its a$$ every time and IF a frog had a glass a$$, it'd only jump once!" Go with as big as you can afford and fit into that space.
2010 WGO Vista 30W, 1993 Geo Tracker
Just a user with no RV or mechanical expertise