Isaac is correct. I had a buddy mill about 1mm all the way around the inside of the steel tray and square the corners off so my SMC 4100 packs would fit. The Orion Platinum4800 and 5000 packs fit the steel tray with no modifications.
yep Orion 3800's fit the oroginal E4 like a glove. many other bumped hard packs dont line up the bumps.