I build bumpers, I make them out of 3/16" and 1/4" steel with internal framework for added rigidity. The Aussies have a killer recipe as well, they use 3mm steel and they have engineered the bends and internal framework to be plenty stout without being overly heavy. Their bumpers are great for the overland wheeler, they offer good protection but they're not super high clearance for rock crawling and they won't take the abuse of constantly dragging your vehicle over rocks and using your bumper to help "guide" your truck up the next boulder.
I have built some rock crawler bumpers for monteros and unless you spend your time door deep in boulders you'd be better off with something lighter. Heavy bumpers increase front suspension wear and decrease milage, it took me some time to get over the "everyone needs a rock bumper" thing. So in the end i 'm having the Chinese build me the overland style bumpers, I'll still build rock bumpers but at the price and for what most Montero owners need they are just too much. I've grown a healthy respect for Montero owner frugalness over the years, the aftermarket has pretty much fled from the Montero world because of all the "we want, we want, we want" and then the "oh, not at that price". Anyone who has built for Monteros will tell you about the time they got burned and i'm no different except the part where i keep coming back for more. Maybe i'm a glutton for punishment.
Sorry that turned into a rant.