Blocking camper in bed...

I'm set-up w a 2002 F350 7.3 Long Bed and a 2003 9'6" Northern Lite Lite series camper.

Has anyone come up with creative solutions to block the camper inside the bed of the truck to keep the camper secured left to right? I've had my camper shift almost 6" while on forest service roads; so need to figure out a system to secure it better than just relying on the tie downs.
I have a 2014 RAM 3500 and a cirrus 820. I made a U shaped device with upright 2x4's. Theres appx 1/4 inch on each side of camper inside the wood, so not alot room to mount but you can tell really fast if you"re getting out of line.
CrazyJane: how far aft in the bed does your blocking run? Do you have it in place while loading the camper onto the truck? Got any pictures you could share?
Mines a long bed so it also has a small area between front of bed and camper. It runs from there to about 4 inches from tailgate area. Ill see what i can do for a pic. Its supposed to rain tomorrow. When it dries out, I"ll take one and post it.
When this first happened to me, the camper moved far enough that one of the tie downs rubbed the paint on the side of the truck. Now I drop lengths of 1x4s between the camper and the wheel arches in the bed after the camper is loaded. The wood takes up most of the space. The camper still moves some, but not a lot. I consider this a temporary solution until I can figure out a better one. At one point I made full length rails out of thicker 2x4s with blocking at each end but it was too tight for the camper to slide between them. The clearance was so little that it was effectively impossible to load the camper.
NuclearFreeZone, I experienced the exact same thing. Crawled up a forest service road in SE British Columbia and the camper moved 6" back on the climb. Then on the way down it shifted significantly. Tie downs also wore in the paint. I'll post a video if I can figure it out... definitely found what we're comfortable to attempt with our set-up... but we love exploring forest service roads while out road tripping and mountain biking; so want to make sure we're secured for doing so.

I was thinking of blocking as you've described but realize that loading the camper would be the trick w any tight fitting jig. I'm trying to come up w a design that would allow the jig to be installed after the camper is loaded; thinking of using a bottle jack to shift the camper to center; then use a module wood system that would drop into place and assume the empty space between the truck bed and camper body.
I also had the shifting problem. Came out and saw camper twisted in bed and since i have a larger gap between bed and camper came to the lik a 2x4 would fit in there. So I went out to pile o' wood and got some scraps. When i got back to house screwed 2x4 onto wood platform. Frame on cirrus doesn't line up with corrugations on bed and noticed flexing of frame. Guessing thats not good for long term health of camper. I get quit a bit less bouncing up and down of camper in bed now. 20181110_104200.jpg