I have Jungle Dawn LED's set in Exo-Terra hoods. These hoods are black plastic rectangular boxes. As designed they sit on top, but I too, would like both of mine inside each terrarrium. The plan is to fit an aluminium screen (and maybe also an "egg crate" plastic light diffuser into a framed inset that can be bolted to the walls of the hood. The fixture would also require a rack to securely hold it.
Complicated, so I haven't started that project yet.
Probably when the summer garden winds down.
Hope you can find an arrangement that works for you with a UV tube.