Other than an occasional Mom & Pop truck stop, I've never been asked to leave a credit card at the counter. With the major brands, you can go in and swipe your card for a pre-authorization amount. I usually over-estimate what I'll need by about 25%. They will give you a receipt for that amount, you go outside (with your credit card in wallet) and fill up. If you don't walk back in to get a final receipt, their equipment automatically charges you only for what you put in. Most T/A truck stops still make you come back in and sign a final receipt (that is printed on old-school dot matrix printers) so I'll avoid those.
Yes, there are cheaper stations out there. If I'm on the road with the fiver in tow and need to get fuel, a truck stop it is. Some actually have usable RV pumps out front and I'll use those if possible. We typically try to unhook on an overnight stay, run the truck into town and fill it up somewhere cheaper if possible. Without an aux tank, though, that leaves us with about a 300-325 mile range the next day. However, we typically will stay under that figure on most drives.
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Given that scenario, the next time you are in a Pilot or Flying J, ask for one of their RV Customer cards. At least you'll get 3 cents per gallon off on diesel at the pump.