Gas tank relocation in a 1969 C30

[kulyeh]

I realize that there is a billion gas relocation threads, however I can't seem to find anything with regards to doing the rear gas relation in anything other then a C10. From pictures of member installation, the C10 rear frame seems a lot different than my C30. The main issue I am coming up against is I don't seem to have a large enough flat area to really get good mounting of the tank. Anyone have some insight into this?