You probably don't need a slider. You also probably don't need fire insurance on your house. Both the slider and the insurance are for those unexpected situations that you hope will not occur.
With the rounded front on the 5er you will be able to turn farther than if it were not rounded, but still not a full 90º. As long as you remember that you will be ok. If you forget, and try to turn 90º, you will do considerable damage to the 5er and to the truck.
2011 Silverado 2500HD Duramax, 4x4, crew cab, long bed
Palomino Puma 253-FBS, 27' 5th wheel
1994 19' Class B on Chevy chassis