I would go the saddle route myself, just personal preference as there is much more room to work with. I am doing it in the future on my '63 C30 dually.
Wherever you decide to put it, try looking at fuel cells on
www.summitracing.com There are lots of places that sell tanks and fuel cells but Summit gives you the option to narrow your search results by dimensons, which is very helpful when trying to find a tank that fits within a certain area.