That cool tube will surprise you, Should be about 10 degrees right there!
I would take down walls are refit the cab if it didnt fit. TBH Everything that is on a micro level if its outside of LED's and CFL's it needs direct cooling and direct exhaust off that light.
Now that reflector you have now its an open bat wing one?
Do you have a outtake fan put up above the light? (Hot air Rises) Then you can put an intake at the bottom...and a fan inside pointed up....Bringing fresh air in the bottom, Pushing it up an removing the hot air up above....Still on the side having your other fan runnin that filter. Totaling 3 fans...Or you get a cool tube, 1 fan for that, 1 fan for intake at the bottom and 1 fan for the filter....
Whats your biggest obstacle with getting a cool tube to fit?