On Sunday, December 11, 2016 at 5:37:54 PM UTC-5, wrote:
Hi, I'm the OP.
Yes, I thought about one of those pancake electrical boxes. If I purposefully wanted to go deeper, I was thinking of maybe sandwiching two pieces of 3/4" azek together, routing a nice trim around the perimeter, and cutting out a 4" dia hole in the center to accomodate a typical 1"deep box. Then caulking around the whole thing against the concrete block.

The reason I want to go with a deeper box is twofold: I'm using 12AWG wire (and I think a pancake box is not deep enough by NEC), and I was also considering dropping a metal conduit down from behind this light to an outlet. This wat the outlet would be on the same switch.

Any pros/cons or other thoughts on that?
Much appreciated.

I was going to suggest something like a chunk of thick vinyl stock as a backplate/surround
for a deeper box. I just never got around to posting it. If you plan to drop some conduit down
to a receptacle, then that seems like the way to go.

That said, why would you want the receptacle on a switch? I'd wire it so that the receptacle
was always hot. Either way, make sure it is GFCI protected.