I have a camper shell that is 8" per side wider than my truck bed. Aprox 120 lbs 30lbs per corner.

I want to use 1/4" thick x 8" wide x 6' long aluminum plate as an 8' wide shelf on top of my truck bed and set the camper on it. The top of the truck bed is 2" inches wide so the remaining 6' would be unsupported for most of the length of the bed at the tail gate end. The front would be supported by the front of the truck bed. Not a problem fastening the camper to the plate or the plate to the truck but will the plate hold the weight?

A 2 x 8 treated piece of wood will do the job but I wanted to use the plate.

That was plan A, then I remembered that I wanted to carry the canoes on the camper also. I can live without carrying the canoes on the camper as they do well on the truck cab but would prefer to put them on the camper. Add 17 lbs. per corner.