Just a standard electric box and a porcelain fixture. The box screws to the top, the porcelain fixture to the box.
You can see that on the right side of the cage is this picture:

Is the MVB you're using self-balasted? If so, those do get pretty hot. I'm not sure if the porcelain fixtures can handle them. Better contact the company.
If not, I do have a way to mount just the fixture part of the dome lights that are so often used with MVB bulbs.
In that case find a 2"x4" metal face plate that has a large circle cut out of it. I stumbled across these by accident.
It's not the way they were meant to be used, but it turns out you can screw the porcelain part of dome fixtures apart and sandwich these face plates between. Holds it very securly.
You have to drill two new holes to get the face plate to fit over a standard 2"x4" electric box but that's not hard.
I did this for my bearded dragon cage and it has held up great. Even survived a 500 mile move in the back of a truck without needing any retightening.
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Current snakes:
0.1 Gonyosoma oxycephala - (Silver/Yellow)
1.2 Gonyosoma oxycephala - (Green)
7.6 Gonyosoma janseni - (Black)
0.1 Gonyosoma janseni - (Black & Tan)