Truck islands almost always have only diesel, no gasoline.
Doghauler has good advice about looking for end pumps and about watching out for enough overhead clearance
Look for gas stations that have the pumps parallel to the road. These are usually easier to get into, but they tend to be older stations - so once again, watch for overhead clearance. Most Flying Js have RV pumps that have diesel AND gas. Most major truck stop chains (Love's, TA, Pilot, etc.) usually have the auto pumps back far enough from the building that you can swing in and out OK.
It takes practice being able to recognize the type of station that you will likely be able to fit into, and it takes practice to know how to best approach the pumps.
I frequently use the MSN Autos
website or Gas Buddy
to locate stations. Then I use the satellite view or Google Maps for an overhead view to see how much clearance there is, whether I will be able to drive around back, how the approach driveways are situated, etc.
Another thing to keep in mind is you may have to be willing to pay an extra 5 or 10 cents a gallon to be able get in and out of a gas station without problems. Stations with higher prices will be less crowded so you won't have to fight with 4-wheelers for space. Five cents a gallon on a 50 gallon full-up is only $2.50, a small price to pay for easier access.