I don't know if your travels will take you to the Northwest and this is kind of a stretch. Costco diesel is inexpensive from the outset and you get an extra 4% off with a Costco credit card. It is the only place I buy my fuel but I don't travel nationally. Not every Costco has diesel and you will have to do some research to pick your places. I guess this may help as Costco probably qualifies as a "club".
Filled both tanks yesterday at $209.9 per gallon. Extra 4% brought it down to $201.5 per. On a recent trip to the coast, diesel was in the low threes. Big difference.