Curmudgeon10

I have a exterior hose reel that attaches to a wooden mounting plate, the plate is attached to the side of the house with standoffs and the holes the standoffs fit though in the vinyl siding are sealed with foam. The problem has been the wooden mounting plate -- I've made three over the last 10 years and Mother Nature/water ALWAYS gets the best of me. It doesn't matter what material, design, coatings I use; eventually my plate fails through joint failure (whether the joints are in between two boards, or I've used plywood with hardwood edge treatments attached with biscuits and Gorilla glue; that also has failed after several years. So this time around, I'm going to use PVC.

I bought a PVC trim board at the home center. In order to make a plate sturdy enough, I'll edge join two pieces about 12" long and attach another pair of edge joined pieces rotated 90 degrees. For appearance only, I'll probably put a small radius on each corner and round over the edges. For paint, I'll use an oil based primer and two or three coats of exterior latex.

But what is the best material to join the material both on edge and when lapping the 2nd piece? With regard to edge joining, should I also secure with pocket screws? What material should I use to fill any gaps?

joecaption

Impossble to tell without a picture, but I can tell you I'd never use any form of wood that's showing to do this job.
What we do is is a meter mounting siding block and run the siding around it. Before installing it we put a piece of 3/4 Advantec subflooring just sitting inside the block.That was the screws have something to pull on.
Mount Blocks and Utility Vents
The box stores most likly will not have these, but any real siding supply company will.
By doing it that way the reel gets attached directly to the side of the house but there's 0 chance of water getting in behind the wall.

Curmudgeon10

That's a good idea, and it would be perfect for new construction. But where I live (outside D.C.) trying to get any trade (other than plumbing and electrical) to respond on a small job is problematic. Problematic in that the only guys who will come out for a small job are often guys you don't want working on the house.

Anyway, my mounting system with standoffs and foam sealant has withstood the test of time (11 years), and I'll continue using it. I found a special purpose bond/fill product that will enable me to construct a mounting plate from my PVC (see: Plastic biscuits, PVC joining, PVC biscuits - Bond&FILL®).

Thanks for your interest.