Rod holder build. Materials?

Jimmy-rigged mod bug has bitten again. I'm thinking about building a rod holder using a plate that will attach to the little cubby in the side of the bed and attaching PVC holders tobit at an angle (seen it on here before, but can't remember who did it). My question is, what material should i use for the plate? I wont be taking the holder off for any reason, so it needs to hold up to the elements. I was thinking some sort of plastic, but not sure where to start. I usually just toss them in the bed and drive, but I'm about to buy a nice rod and reel before springtime. any help would be appreciated!

 

I made one that has the back made of wood.
I made mine with the intentions I would remove it when not in use, however, I fish too often to take it off.
It has held up well to the elements so far (~3 months). It is pressure treated plywood, 3/4 inch I believe, it was scrap I had laying around.
I used 2 inch PVC for the rod holders (scrap I had), I probably would have gone with 1.5 inch if I had to buy it.
One is placed at 45* the other a little less to give the rod tips some wiggle room.
I just guess-timated the distance between them, using my largest reel as a reference.
2 holes were drilled in each pipe, and two bolts attach the PVC to the wood.
Krylon Fusion'd the whole set up and attached.

I can post pictures when I get home if you would like.