is there a crown in the 8 ft box on 16 gmc

I checked my 2012 6-1/2' box with a long level this spring, there is definitely a crown in the middle of the box, so I'd say all 2011 and newer GM's have this crown in them. I could not see the crown, but the level does not lie. I put two semi truck mudflaps under the back half of my rubber bed mat and my camper now stays level. I noticed looking at photos from past years and I can see that at times my camper looked tilted to the rear, other times level, so I raised the rear bed mat to stay level.

Heck you can see it in the picture in my signature block. Here is a larger copy of the same picture (sorry it wasn't straight on from the side). Look at the camper line and the truck box and see the taper to the rear. The cabover looks leaned back also, but the truck roof slope may make it look worse than it is.

Older threads suggest that the crown exists, but I think a horse stall matt from Tractor Supply or similar should take care of it.

I have a bed mat in my truck bed and then I added a 12" deep X the width of the bed 1/2" thick rubber piece in the back of the truck bed to help compensate for the crown.

jimh425 wrote:
Older threads suggest that the crown exists, but I think a horse stall matt from Tractor Supply or similar should take care of it.

Maybe for some, but in my case no. I've had Tractor Supply horse mats from day one, but had some slight rocking/ porposing on certain sections of road. I had to add rubber strips 3/16" thick, 12" x 48" front and rear to help compensate for the crowned area. Rides possibly a tad bit better (less porposing) , but sometimes wishful thinking influences percieved results. At the very least, it sits level.

I've been over this issue of the crowned bed and the porpoising effect and fighting it for the past year.

I've got all that stuff on my truck, air bags, stableloads, new bilstein shocks, front timbrens, rubber pad, and pads to level the bed.

Maybe it's better, but I still have problems on rough roads - especially concrete. I've decided that the camper is just too heavy for the truck - and it's a 1 ton truck.

Wonder if poly foam insualtion board might help- crush to conform?

I havent used but others have, mostly for raising camper, so maybe they might chime in on other aspects of using the board.

I already have a rubber mat in the box.

That is very strange.

Possibly if one were to put some 1/4-1/2" spacers under the front and rear bed mounts, and leave the middle bed mounts unspaced, this longitudinal bow could be taken out of the bed floor...

Jim&Carolyn wrote:
I've been over this issue of the crowned bed and the porpoising effect and fighting it for the past year.

I've got all that stuff on my truck, air bags, stableloads, new bilstein shocks, front timbrens, rubber pad, and pads to level the bed.

Maybe it's better, but I still have problems on rough roads - especially concrete. I've decided that the camper is just too heavy for the truck - and it's a 1 ton truck.

Is your truck a DRW?

Wondering if it would be possible to put some kind of support,, 2x4 or such,
on the sides of the truck bed to have your TC sit,rest directly on this..

My camper sits just like that bolted to the sides of the box,not even touching the bed bottom and doesnt move at all..