Do not ever use the stuff in the spray can.
Roll on might be alright if IT HAS A SEPERATE CATALYST.
If you have an air compressor or can rent one (5hp or bigger) then I would suggest going to ebay and search for "bedliner" or bed liner and you will find good kits you can buy. The same stuff as the shops use that would charge you $300 or more.

The good kits will come with a seperate catalyst usually premeasured for you to mix. THey will also come with the spray gun to attatch to ur air source.
This way you can adjust gun and air pressure to spray on the desired thickness, texture, and finish.
I would suggest a light sanding of entire bed before spraying.
Its a great side job for extra money too.