I've been trying to decide how to line my bed, and the Line-X and Rhino shops in the area want over $500 to do the job. I've researched opinions on Al's Liner and everybody that's tried it seems to love it. ...and at half the price of Line-X for a double thickness coat I'll be happy to spend a day prepping and spraying.
here's one of the larger forum threads I've found talking about it. Its 20 pages long but basically it sounds like as long as you're reasonably competent and follow instructions its a great product to apply and use.
Al's Liner DIY Spray In BEDLINER kit.... - Dodge Cummins Diesel Forum