...I see no reason to remove it from it's original location on an AD.
Me either. I've made a whole bunch of changes on my truck and leaving the battery where it was is a no-brainer, it's actually a nice handy place for one.
I didn't have a good original box/tray and wanted a little larger one so I'm using one of the stainless drop down boxes sold by the aftermarket/hot rod shops for these trucks.
In my other truck I made the original longer by moving one bracket back and making a new bottom.
Grigg