I have been using Nightscaping Vermeer fixtures for inground applications for a few years now. ( I have a few Intense Lighting fixures in too) and have been very happy with their thermal management. They are a sealed, cast brass fixture that uses MR16 Lamps (not PARs).
In many jobs I have installed these in pine needle laden forest floors with no issues at all. (tinder dry in the summer)
I have used the Nightscaping thermal breakers on a few occassions and have never yet had one fail.
Have a great day.