what is the longest rolling shop cabinet you have built? i don't want to permanently take more wall space out of my shop.i was thinking of a 6 ft. cabinet on wheels and putting my 12 inch slider on top with shelves on the bottom.i am thinking of plywood like a normal cabinet but I wonder if I need to build a frame under the box to eliminate sag or use 6 wheels to spread the load?any one build one this long or longer.any input or thoughts appreciated.