I assume that you've seen mine, but just in case here it is. I bought rack rails and mounted them inside the wooden cab... they go all the way top to bottom. I put in a solid shelf... reinforced the back of the shelf with two small L brackets. The bottom of the mc50 is directly bolted to the shelf. It's pain to pull the mac, but once serviced (as yours has been) they are very low maintenance... just need direct access to the power switch and (occasionally) the volume knob.
SInce this picture I've cleaned up the wiring and put the power switch at the very back... and acquired a padded road case for the whole thing (which my 1x15 pine cab and JBL sit on top of nicely.
The two outside handles are a must. It's really too heavy for a single top handle.