Not only is this chest XRAY proof to a certain extent, it also just looks plain cool. Simply place a redstone torch on the "desk" and watch as the floor is pulled downwards. and then retracted into the wall, revealing a chest. Simply remove the torch to open it again. With my experience, many XRAY packs and mods have a slight flaw, anything near/obstructed by a piston will be come invisible, as well as the piston itself. Enjoy!