Too sharp a turn with short bed truck.

[5ER]

We are taking our fifth wheel out for the first time in two days for practice and need some comments back on turning without using the slider on our hitch. Is it possible to make too sharp a turn going forward that the Truck cab and trailer would hit? Never heard anyone say they new of someone doing this, but I don't want to be the first. I am also concerned about hitting the cab backing up. I would hate to hit the cab with the trailer and have my wife say "See! you should have used the slider". How do you know how sharp you can turn before you need to use the slider hitch.
This is going to sound dumb. They should make something out of styrofoam or something similar that you put on the corners of your truck cab just for backing up, so beginners like myself could practice with. If you did make contact it would make a noise before damage. Anyway you can see that I am feeling anxious about pulling our new 5ER. The last time I pulled something this big was a long time ago in the Army and I wasn't this anxious, maybe because I didn't pay for it. Thanks for replies.

Rodger & Brenda, 2 Pekes Poogan & Jenny
2003 F350 Dually PSD pulling 2003 3295RK
Dunbar, WV