that plate should work much better than those little gray thermal strips!! i like your solution because as you said, a bigger heat sink wouldn't work if it relied on air flow inside the housing... since your plate (still a giant heat-sink) is tied TO the housing it can dissipate heat through it. it's very cool (pun intended)
I wondered if there's an issue with bonding the light board's back plate (via your copper disc), but - and I'm no electrician - I think it's ok? I don't have one of these installed in my pool so I can't check how it worked with the thermal strips (they are conductive, not insulators)... but it looks like the strips and brass mounting posts bonded it to begin with, before your mod?
I wondered if there's an issue with bonding the light board's back plate (via your copper disc), but - and I'm no electrician - I think it's ok? I don't have one of these installed in my pool so I can't check how it worked with the thermal strips (they are conductive, not insulators)... but it looks like the strips and brass mounting posts bonded it to begin with, before your mod?