It looks like you have good clearance from 5th wheel to bedrails.
Next time out just do a test turn to see how close it comes to touching.
The only problem that I might mention is when backing up a hill with a tight turn... then the Box may come too close. (?)... and that is not very often.
I have a similar truck, however I have a black PacBox that sits flush with the bedrails.(by choice)
I find the Box to be so handy to carry secured items.
'07 WildCat 30 RLBS ~ West Coast Edition ~
Trail Air - Tri Glide Pin Box
2000 F350 Lariat DRW 4x4 7.3 Diesel 89k miles
Edge programmer, 4" SS exhaust turbo/back,
Tru-Cool Max Trans Cooler, Bilstein Shocks
Vancouver Island, B.C., Canada