I did what AidenJ did with 6" pipe capped on one end and threaded on the other. Also drilled drain holes in the bottom. Additionally, I drilled a hole in the threaded cap and keep it attached to the bumper with a short piece of rope so I won't lose it if it comes off in transit or I forget to screw it back.
Keith should tell you what type of paint to use. I had some minor repair work done and the repairman gave me a pint of what he used but it doesn't have the recipe on the can.
Enjoy your NL. They are fine truck campers.
I haul my drift boat to the Rockies in May and stay for 3 or 4 months in my truck camper. Although I could launch the boat with the TC on, it is much easier for me to launch the boat with the camper off the truck. I have electric jacks. As your experience loading/unloading the camper increases, the time required should decrease down to about 15 minutes. I try to stay at a campground central to several rivers so I don't have to move and load/unload too frequently. After unloading, I lower the camper as close to the ground as feasible. The lower center of gravity really helps with stability. The manufacturer of my camper says it is not necessary to support the camper floor when its off the truck. Check to see what the manufacturer of your camper recommends.
Several of the rivers I float have narrow, steep, rocky, tree-lined and sometimes muddy accesses that aren't paved. Some accesses require backing down onto gravel banks. I wouldn't want the camper on using those accesses even though my truck is 4 WD. Leaving the camper at the campground, it's probably less likely for someone to break into the camper than when it's parked at the access site before or after shuttling. Having the camper off the truck and leaving the boat at the campground allows me to use the truck to get to some out of the way and lightly fished waters if I want to take a break from floating. I do keep the camper on and leave the boat at the campground when I know I'll only be wading easily accessible streams for several days in a row. I get excited just thinking about getting back out there.