Arcadia have a reflector hood product called a SLIMLINE LUMINAIRE that is designed to mount inside a tank (attached to the ceiling with screws if the ceiling is timber) , these come in a range of lengths (I suggest you get a hood that is NO MORE THAN 2/3 the length of the tank (so no more than 3ft long in your case).
These Arcadia luminaires come with either a T5ho 6% UVB tube , or a T5ho 12% UVB tube , or a T5ho 14% UVB tube in the price already installed , so it's essentially plug-n-play.
This will help work out the strength T5ho tube you need for your setup based on distance to the basking spot :
viewtopic.php?f=34&t=235611
If your lid is a mesh lid , mounting under the mesh lid is simplicity itself, all you need is two nylon cable ties of appropriate length to essentially form a loop around the hood , one at each end.