I've never seen an 8 foot tall drum. I have, however, seen huge stacks of drums (my dad works in the pigment industry, so they'll have them stacked to the ceiling, but usually with some kind of shelving type units). That said, you could probably stand to knock off a couple rows of barrels there, or possibly aim for somewhere in between (though that makes alignment a lot more difficult, but texture locking is handy).
Oh, and I forgot to mention with that tread stuff -- it's typically bent around the edges and welded to a more solid stucture, so you'd want to put a tread textured brush on the sides, too. I couldn't really find a good picture, but this sort of gives you the idea:
http://www.partnersengineering.com.au/perforated-metal.htmlAlternatively, you could treat them like plates set into a more heavy duty frame.
Edit: An example of what I mean:
