Building a mirror cell is pretty easy, and for most purposes, including imaging, cells like the Stellafane design works really well.
https://stellafane.org/tm/dob/ota/cell.html
https://stellafane.org/tm/dob/ota/cell2.html
I used this design to build my mirror cell for my 10" imaging newt, and it has been fantastic. I checked the design using PLOP and adjusted my radius supports slightly. If you use quality marine ply and clear finish it you will have a beautiful cell, much nicer than just another aluminium one. And you can mount the base as the rear bulkhead of your tube.