If the pump stops at say $75.00, all you need to do is put pump nozzle back, print your receipt and start a new transaction. It will go until you stop it or another $75. You can also go inside and pre-pay for say $150.00 of gas and if you are full at $120.00, the credit is immediately returned to your card (if it's a debit card I know for sure). We have done this many times and if I look at the account 5 minutes later that credit has been redeposited already.
We use gas buddy and fill and most regular gas stations. We are 36' pulling a trailer with motorcycles, so about 45' total and have no problem finding stations we can use. We use google earth and take a look when we find the cheaper gas price (on our route) to make sure we can fit first.