I built an octagonal flower box with a raised bottom to sit on top of my
inground filter to conceal it. I then placed my Fido Electric Fence
controller inside the box. The plan is/was to put an insert inside the
remaining space to plant flowers and conceal the Fido box.

The box has been sitting outside for a couple of weeks on top of the filter,
with the Fido box sitting inside. Even though I stained this thing
thorougly, the bottom plywood has warped already. I used pressure treated
wood for the sides, so they are OK. I knew this would happen eventually, but
the top insert (finished now) would help alleviate this. I also planned to
drill some drain holes in the insert and the outside planter in an area not
occupied by the Fido box.

I don't want to redo this thing this year. so I'm wondering if some
fibreglass resin will seal this thing well enough for now to prevent further
damage? Any other ideas for water proofing? Does not have to be pretty,
since it won't be visible from the outside.