Is an old Class-A affordable to drive?

I have had RVs since 1989 with trailers, popups and 7 motorhomes. I bought a '75 GMC last year for $10K thinking I would put another 10 into it. I now have $29K in it and it is almost finished. I now get 9 mpg on it. I also have a 1995 Roadtrek 19' that gives 17 mpg. I had a '03 Mountain Aire for 11 years that would 8.5 with a car in tow. After my DW died I could not manage the 6 steps up and that is why I got the smaller ones. They are very enjoyable but expensive.