full time... no fixed base..... um
I think a full sized bus, like ex greyhound kind of thing..... detroit diesel straight six 71 called a 6-71, 6v71 or 8v71 are my picks... older all mechanical diesels, you can still find all the parts for them...
Older ones like from 1940's made by GMC up to some newer ones made by Eagle or mci......... the shortest I have ever seen is about 32 feet long, the long ones are what 40 feet?
brake, steering, suspension all big stuff like semi truck kind of big, but you also have the most storage underneath and room inside.
suggestion... go to you tube... look for videos made by a guy called "bus grease monkey" decide if these things are a right fit for you.