My Camp-X has rubber footings around the perimeter and was not intended to sit on horse mats. However, my F350 has a higher cab than most 1/2 ton trucks and I needed to add horse mats for clearance. It appears the mats and rubber footers are compressing more close to the cab and I just needed to shim that area up more.Did you measure your pickup bed rails from the floor of the bed to the top of the rails at the front, middle and rear of your box? Curious if that year F350 has different rail height from front to back. Also, how does the cabover angle look compared to the cab and rest of the pickup? One side effect of angling the camper may be making the cabover/roofline angled compared to the rest of the truck. If the cabover looks angled too, then perhaps it is sitting uneven on the brackets or horse mats/runners. I used cut lengths of horsemat on mine. Didn't use the whole mat, as the installer did, because the whole mat weighed about 90 lbs if I recall correctly for the 50" width. I cut just the strip width I needed (about 5" wide and 6.5' long) to support the extrusion. OEV confirmed that the support needs to be around the footprint perimeter (extrusion) and doesn't need to be in the middle of the floor (and, importantly, should not be higher in the middle of the floor than what is supporting the perimeter extrusion).