Do You Use Centering Blocks/Devices?

I use wood blocks bolted to the bed floor on each side in the front of the bed.

I use wood blocks to keep the camper centered.

I wish I had 2" of clearance. I have about a half inch. I leave the camper on the truck and have only had to load it 4 times in over 6 years. I finally found a solution to loading. At least I tried something new last year and had instant success. I will soon be reloading again so I have my fingers crossed. Last year I used a $40 laser level from Lowes. The laser level is about 8" long and has a strong magnet on the based. I attach the laser to the wheel well and have a mark on the camper. As I back up I keep the laser aligned with the mark. I do have to stop a couple of times to point the laser higher. Of course, I also have to remove the laser level before I lower the camper into position. Last year I loaded exactly on the first try.

I have seen a description of V shaped blocks to guide the camper into position. I would think twice about using something like that. The jacks and brackets are not designed to have a strong force pushing sideways. I would be concerned about tearing the brackets from the camper or bending the brackets or jacks.

BTW, after loading I place boards on both sides between the camper and the wheel wells. This would prevent any sliding or shifting in the truck bed after loading.

My camper has a nylon or dense plastic bumper in the front that contacts the bed of the truck and prevents the camper from being positioned too far forward. I found I need a bit more clearance and used duct tape to attach an additional piece of 5/8" plywood. I should probably just permanently attach the plywood.

My camper bumpstops allow the camper too far forward, contacting the top of the bed.
I just stand a 3" spacer, ( 2 -2xs nailed together) against the front of the bed.
If you wanted to close the gap on the sides, make 3/4 of a picture frame out of the front spacer and a couple 1xs or 3/4 plywood.
Fwiw I've not noticed my camper shifting side to side at all in many miles of bad roads.
Then again, it's heavy enough that it's made its own indentations in the truck bed! Prolly helps keep it locked in!

I don't use any, but if you search the archives, you should be able to find some.

I stood a 2x6 on edge the width of the bed at the front.
Then, I cut 2 pcs of 6x6 about 18" long at an angle and screwed & glued 'em to the ends of the 2x6.
The angle guides the TC to center when backing under it.

If one 2x6 is too close for comfort, use 2 of them. This will give you about 2" of clearance between the front of the TC and the upper front edge of the bed.

Works like a charm for me.