I spent five summers selling merchandise for a traveling music group and got to be an expert at touring the country driving a box truck with a trailer. A couple of suggestions:
If you have to stop, only stop at truck stops. There's almost no way of being forced to back up in those places. If you don't need fuel, pull into the truck parking. You can just drive straight in and out of those spots. If the truck is a diesel, check to see if it will fit a fuel nozzle for a semi truck. If not, you will need to fuel up at the auto diesel pump.
It can take a while to adjust to the extra size of the truck. If you are in the right lane and there is no shoulder or, worse yet, there is no shoulder on either side don't panic. Just keep your sight line on the highway line to your left. If you try to drive in the "center of the lane" you will drift to the right and possibly hit something.
If you get in a jam and have to back up get your girlfriend to be your spotter. Have her stand where you can see each other in your driver side mirror to stop you if you are about to jackknife or hit something.
Backing up doesn't have to be scary. Keep your hand at the 6:00 position on the wheel. That way you just move your hand in the direction you want the trailer to turn. Hover your foot over the brake while you back up so you won't accidentally panic and hit the gas. Practice in an empty parking lot first and you'll see it's not too bad. Go slowly. If some jag-off runs over and starts shouting directions at you while you are backing up give him the finger because he's a dick.