I have a 35ft 5th wheel and diesel truck. I use the truck lanes because they have tons of room to maneuver with no cars around. No stress for me. My wife even is comfortable pulling into or out of the truck fuel lanes now when she helps with driving.
The diesel prices do seem a bit higher than if you get off the highway, but the convenience is well worth the extra cost for me.
You just follow the truck entrance signs (follow the big trucks :) )and pull into an open fuel lane (or line up behind a fuel lane if all are full. Just drive slowly and be courteous to the other big rigs in there - they are mostly professionals and I have found it quite easy driving among them.
If you pay with cash or a major credit card (like we did for the first 6 months)... you will first need to walk inside and pay (after you pull next to the pump). You then pump the fuel and/or DEF. When full, pull forward so the truck behind you can start fueling. Then you go inside to get change if you paid cash or the final receipt if credit card is used.
My wife got tired of having to walk inside to do the credit card payment thing so we got the Pilot/Flying J charge card. Now we "pay at the pump"... just pull in to the fuel pump in the truck lanes, put in the Pilot/Flying J charge card, enter my pin number, select "tractor" and sometimes also "DEF". Fill her up and leave.
Sometimes I pull forward after filling up and run into the bathroom if necessary. If there is a truck behind you, it takes them at least 5 minutes to fill up so I always leave before they are ready to move.
Ed
