use a trooper tank, where the spare tire goes that will give you 18 gal usable gas with a 2 or 3 gal
reserve.
ive put 21+ in my trooper at once but it was missing as a pulled up to the pumps
a stock short bed tank would be about 13 gal in a short bed.
84\85 trops have a mid ship 13 gal tank
86\87 would be carbe start of the 20 gal tank.....
88 up EFI, un less its a 89\91 trop with the GM 2.8L V-6
in my 86 long bed ive thought of adding the trop tank, plus the OE long bed tank making 37 gal with a 3 gal safety net.
3 gal will take me 60 miles with a ton of cargo, not so by any means with a V-8
