Its welded to the bulkhead by spot welds, if yours isnt too rusty you should be able to feel 'em, if not then its down to the good old hammer and bolster (big thick chisel). You should be able to get under the tray and prise it up to reveal where the spot welds are, then use a spot weld drill bit to drill em out. Try not to got all the way through the bulkhead but its no big deal if you do as you can buy the tray with part of the bulkhead already attached.

good luck