Our rig is 24 feet long but we tow another vehicle all the time.
We buy our gas at stations advertising the lowest price. Brands are of no concern to us. The lowest price is often found at regular size stations, especially when off the beaten path. It takes fast planning moments ahead but we do fine.
A 30 foot rig not towing anything will be much easier at regular gas stations than our 6 foot shorter rig but towing. Just watch your mirrors. A back-up camera helps too. If travelling with another set of eyes, have them stand outside and "spot you" until your confidence builds up. After a while, you'll get real good on your own.