Sorry, I don't know your rig, but assume it's diesel...Most Truck Stops won't let you pay at the pump in the truck fueling lanes, so you have to go inside and prepay. The auto-diesel pumps will have PATP and you'll even find some dedicated RV pump stations, also PATP. I'm towing 4 wheels down and go to the truck lanes so I don't have to possibly back up.
Compare fuel prices at:
http://autos.msn.com/everyday/gasstations.aspx
Generally, you'll find prices at stations that match truck stop prices with any discounts. Trucking Co.'s have accounts with pre-quoted fuel prices, but I don't know about owner-operator accounts. I've had personal Loves, T/A, Flyin J discount cards, but could never use enough fuel to take advantage of discounts. Discount card pay methods could have changed...been years since I had one.