Great idea. Sold my 71 Dodge Travco 44k original miles 413 motor a couple of years ago. Great vehicle. 7mpg. 8 on a good day. I doubt you're going to get 10mpg on any motorhome other than a few diesels.
When I moved across country to go to graduate school years ago, I bought an old International ambulance with a blown 288 engine for $150. Bought an old pickup with a good engine for $100, swapped it in, bought a towbar and pulled my Camaro from NY to Colorado with all our possessions packed inside. Sold it for about $800 when I got here.

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1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13