The buses made for long distance travel would be better for a conversion. Shuttle buses and in town buses are not set up for the long hills like a over the road bus. They have the storage under the floor for the needed stuff genset, batteries, mini-split HVAC, water tanks, propane tanks, and more.
I'm set up with 180 gallons of fresh water, 120 gray, 60 black, dual propane tanks, mini-split HVAC, inverters, Onan genset, tinny Honda genset, and more and still have more than half of my pass though bays. I could of gone with smaller tanks and a single genset, but I wanted to be set up differently.
I'm able to get into any campground a class A can fit into. With not having fiberglass walls or rubber roofs it's a huge issue if I hit a few branches getting into sites or a the road. With not having AC on the roof I'm not as tall as a lot of class A's or 5 th wheel's. I have no issues with pulling my toad on long hills, live / work full time so we carry a lot of stuff, and I'm way under my max weights. I do have issues backing up my toad 4 wheels down, but most people do.
I get 8.5 to 9.5 gpm. If you keep everything in good shape stuff dose break, but if you keep everything in good shape they will last 700,000 + miles. A huge down side is a lot of shops will not do an “I frame rebuild” on buses so it will have to be pulled out, but you should know when one is coming and be able to schedule the work with who you want.