If you're concerned about where to fuel, given your lack of experience I'd totally suggest takin a couple shorter trips to get used to towing the rig and everything that goes along with it.
It'll make your long trip more enjoyable and less risky.
Regarding fuel, you could pick up a used slip tank for a few hundred bucks and put it in the back of your truck and pack an extra 40-100 gal with you negating the need to stop for fuel.
Of course there are worse places to pull into than big freeway fuel stations, and you gotta pull over sometime, hence the practice runs suggestion.
Have fun with your big rig!
