I've decided that longevity is pretty much a non-issue with either PT or steel, thanks to all the posts on this thread. Thanks, for everyone's input.
The various advantages and drawbacks of PT vs steel are not so compelling for my useage to sway me one way or the other. In other words, I think I would be happy with either one.
Last week I called the steel yard for prices. I also asked about availability, but they didn't have 4 sheets in stock. Then, I shopped Home Depot for PT. I looked at 2x10s which sold for about $15 for a 16' length. It takes 8 pieces to cover the trailer bed, ie about $120 worth. Maybe I'm just too picky, but I couldn't find close to 8 good quality boards. I must admit I got tired of looking before I got to the bottom of the pile.
Four sheets of steel costs $252 plus tax. PT costs $120 plus tax. The trailer shop might install the PT for $40 if I supply the lumber, but I didn't ask since I couldn't find decent boards on my visit to Home Depot. I maybe could have found good boards at Lowe's or elsewhere, but I get tired real fast looking for good boards in a stack of construction grade lumber.
Anyway, I took the easy way out. The steel yard got a shipment yesterday. I bought 4 sheets today and dropped them and the trailer off at the shop. Tearing off the old boards and installing the steel sheets is $40. It should be ready to pick up in a day or two. The installer said he would even paint the bed for free... as long as black paint was OK with me. Heck, black is fine (my trailer is red). I don't usually color coordinate too well anyway.
OkieG