I posted this on TGP as well but i wanted to get the opinion of the Marshall experts. I have a JCM 800 4104 that i really like the sound of. I replaced the V30's thatwere in it with ET65's and it made a huge difference but I still much prefer it though into a 212 closed back cab. I'd like to make the combo a closed back but instead of butchering the original white combo i thought i'd get a new closed back combo cab made. I have a guy that makes cabs looking into it as well. I've looked at some closed back combo's such as the 5150 and Mesa Roadster and they don't seem much larger than mine other than a couple inches taller and a few inches deeper. I'll need to keep the top part open to allow the tubes to circulate of course. Does the depth of the cab make a huge difference in the bottom end? Most of the closed combos seem to be about 12 inches. Has anyone ever done this before? Any ideas?