out of my element

I'm all for being prepared, so just to be sure, ask the seller to measure the height of the short wall under the wing, and a measurement from the bottom of the camper to the underside of the cabover for you. Compare that to the depth of your truck bed. If he wants his money he will be more than happy to do this.

Map out the closest big box or lumber yard just in case you need to run out quick and pick up a stack of 2x4's for the trip home. You can build something permanent later if necessary.

No you shouldn't need anything.

I have had TCs on NBS Chevys (up to 2007) and NNBS Chevys (2007.5 through 2013). None of them needed anything to clear the bed rails.

On our current combo '12 Chevy 2500 and '13 Eagle Cap 850 has about an inch clearance between the camper wings and the top of the bed rails.

From what I have read, you can either build a platform out of 2x4's, 2x6's to raise it up. Another option is using rigid insulation. The roof clearance issue is talking about the cabover clearing the roof of your truck.