Just to answer your questions the frame inside is constructed of 2x3's. Sagging will not be an issue for the front or back. I have looked at numerous stands made buy all-glass etc and they construct most of theirs using 1x4's which fair weaker in structure standards ( i work at menards exactly like the HD
here but bigger). The back is supported by the middle brace as you can see in the pic, the front is supported by 2-2x3's right at the edge of the finished plywood you see in front. Plus all the support from the plywood.
As for the rubbermaid container...The doors are large enough for it to slip right out its only in on the inside of the door braces by about 3 inches each side. So by sliding it inside the stand and pulling it forward it will slip right out! I will get some pics of doing it to explain better.