Perry,
I'd suggest that you check your truck's Owners Manual first - towing a 5th wheel may not be recommended.
There were (at least for 2006, as an example) some *Foot Notes* on the 5.8 ft box configurations.
Note: "Fifth-wheel or goose neck trailering is neither designed nor intended for this vehicle."
Of course, I don't know that this applies to all model year's, I simply remembered reading it in our 2006 GM manual.
If 5th wheel towing isn't an issue, and given the length of the truck bed, you might also want/need to replace the pin
box with a Sidewinder (or similar) so that you can make tight turns. Just some food for thought.......
Terri, the Chevy co-pilot