I have an Mxt, but in the semi-custom depth, half way between the two stated depths on the web site. It's semi-custom because it is a standard depth, but he doesn't list it on the web page. He already has the jigs and such.
The capacity is accurate. I have 100 boxes (counted them this weekend) which includes several 50 cabs.
I have put some under the bottom shelf because if the humidity spikes, it will spike highest at the bottom and having the buffer is a bit of peace of mind; plus, I already owned the beads.
The taller the cabinet, the greater the RH differential between top and bottom. Mine has been 4% higher at the bottom since I got the cabinet. I have a couple wireless oregon scientific RH gauges, one at the top and one at the bottom, which I swap about every two weeks. The one at the bottom always reads 4% higher than the one at the top.
Based on this, I am considering moving my singles tray lower in the cabinet, maybe just have one shelf below it.
here's my cabinet
This is what it used to look like empty
