I have yet to build a LPG, but I did use a surface-mount humbucker on a resonator build earlier this year and I'm currently working on another build where I'm trying to utilize one. They're easy to install and I think it would work great on an LPG. I should note that you still need to drill a hole to get the wires down into the control cavity, but that's much easier than cutting a hole so the pickup can protrude thru the plate.
From my experience (which is limited), the main concern with surface-mount pickups is the distance from the strings. You need to factor in the thickness of the license plate, pickup, and mounting tape to ensure it doesn't hit the strings. If the pickup is too high, you have to raise the bridge/nut to get proper clearance. If it's too low, you may be able to shim the pickup to raise it, but its certainly not as easy as it is with the adjustment screws on conventional pickups.
All of that said, I think its a really good idea, just be aware of the distance between the pickup and the strings. As long as you have that covered, I think it will work great!
Thanks for the reply. So there would be no interference mounting the pu on top of a metal LP?
I recently put 2 MGB flat buckers on an LPG, only had to drill small holes for wires and cover plate screws. Decided that the small amount of damage was worth it, and it truely was!!
Those Flat pickups are wrapped up pretty good, so there shouldn’t be any problems mounting it on metal?