My parents just bought a very similar rv earlier this year and drove around the country with it over the summer. I think it was a 26' Shasta on a chevy chassis. 350 small block but with a 3 speed no o/d. I think they got around 6mpg.
Aero is going to be easy as cake to improve on that thing but i will say with that age, dont forget to fix the a/c.
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