Our Class A Diesel Pusher gets about 8.5mpg, towing a 2008 Chevy Colorado 4x4 pickup. Many national parks have large enough sites for all size rigs, it depends on the park. We found state parks are more limited on size but there are still lots of state parks to choose from that you could fit into. We also camp in Corps of Engineers Campgrounds. You can look at NP and Corps of Engineer spot sizes on www.recreation.gov
For example, St Mary Campground in Glacier NP has 3 sites that are 40' long and their campground books up well in advance. We full time in a 33' Class A DP with 2 slides with no problem. It depends on the floor plan.
We like the Class A because I as the copilot can get up and use the rest room and get a beverage while we're on the road. When we stop we start the generator and if the weather's not nice enough to have a picnic outside, we can have lunch inside the RV comfortable. The cons are maintenance of 2 vehicles but since you already maintain the bike, that shouldn't be much different. Another con is that a large Class A won't go down dirt or gravel roads and dispersed camping places as well as a TC.