I would start by findind a 99-03 shortbed extended cab F-250 as these have the same wheelbase as a excursion.Then see if anything close to the tank would be affected by 140-170F heat.It would have to be a plastic tank,as oil heated repeatly in a steel tank will cause polymerization of the oil (turns it to a plastic type grit which is no good for your truck).If you don't mind sacrificing cargo area,a plastic marine tank can be bought and modified for around $100-$150,depending on size(i would get a 15-25 gallon flat transluesent model as you can see fuel level easily thru tank........good luck .
