YotaTech Forums - remove truck bed

I have just started my first big automotive undertaking, and I have a couple questions, I have an 87 custom cab truck. Tonight I removed the bed and found that the bottom or underside of the bed has a black textured liner on it. Is this toyota factory that is on all trucks, or done afterwards?Possibly by the company that installed the custom cab. I was going to paint the underside with rust bullet but I do not think I can any more as this stuff won't come off. The stuff is still on there well except around the wheel wells.
Also on the six posts that support the bed I found three square rubber "washers" are these factory. They look kind of cheapo. Should I reuse them or is there something else that I should use instead that would be better.