FWIW, I have a large front access door, and a back door that takes almost the whole back side, plus two hinged CPs (and one fixed) on my rotating CP assembly.
(http://www.1uparcade.com/images/cabAssembly.jpg)
The image above shows the basic frame, all that's missing is doors, panels, and bezels. The whole thing is braced by two 2x4s across the top (visible in the pic, one where the back dolly handles are, one above/behind the marquee light.) There are two more 2x4s across the base, underneath the floor of the cabinet. The cabinet floor, the front and rear kickplates, and another plywood board on the very underside of the cab (under the bottom set of 2x4s) form a strong wooden box that provides most of the cab's strength. The monitor shelf (cross-braced by two 1x2s) and the speaker plate and top panel also add rigidity.
There might be better/more professional ways to do this sort of thing, but this design has proven to be quite sturdy, despite the relative lack of front and back bracing. The whole thing feels very solid while being moved on the built- in casters, and does not shift or wobble at all during game play. If it really worries you, you can always split the back 60/40, and have a smaller rear door for just the monitor, and a larger fixed panel across the bottom half, but I find my configuration allows more convenient access to the PC thru the larger rear door. YMMV.