Thanks for the comments.
I think you could scale it up for 6mm. A slightly larger mesh, or maybe the same mesh but having longer strands as the 'tree trunks' could do the job. If the trunks need thickening, then sliding a length of electrical wire insulation over the trunk might be an option. using the canopy from a commercial 6mm tree, removing the trunk and sticking the canopy on to the scourer might make the covering look better, or maybe the sisal/wire approach for conifers could work. If I can summon up the energy tomorrow I may have a play with some bits and see what it looks like. doing something fancier on top might make it a bit more fragile and so sitting troops on top might not be an option.
Al