I'm looking at buying a box truck and using the box bed to put ads on. I fgure on having some rails welded to the outside bottom of the bed, and half way up, to hold plywood sheets that I would then paint the ad(s) on. I want to be able to change the ads, so I don't want to paint straight onto the bed, hence the plywood. I'm trying to keep costs down. A sheet of plywood is about $18 I think - 4 sheets per side - $80 3 gallons paint - $50 welding cost - $250 ? So, it would take about $400 to do, if the welding cost is close to accurate. Anyone ever done something like this before? Is there a better material to use than plywood? Insulation board seems to weak to take the time to paint an ad on, just to see it crumble.