Basically finished up the mods to the tray for dual battery/master relay today. You can see in the pictures below some weatherstripping to take up some slack and also the angle extension needed to accomedate two master relays. I also ordered a 8 fuse ATC style fuse holder to mount on the opposite side of the battery rack to supply power to the always hot items such as interior lights, clocks, and one of the ignitions. I'm also short a couple of nutplates to mount the masters so I added it to my list of stuff to order.
Tray finished, you can see the angle extension and weatherstripping for snugness.