Well the frame is made of 1" square tubing, has polyethelene sheeting on the exterior, 1/8" plate steel for the hinge plate, and lift off hinges. I made the latching system from all-thread and some springs and nuts.
It sounds like a homemade concoction of redneck proportions, but the prototypes have been on my Prowler for 8-9 months and held up great!
Hey Cub, those doors look good! I went a slightly different route, by using 1/2" thick HDPE sheets (from www.modernpastics.com, about $150 for two with shipping). The hinge plate is mounted to the cage frame by a piece of 1/8" by 3" flat bar, cut and welded to mimic the chevron shape in the cage. The hinges are marine hatch hinges, which have easily-removed pins. Can't remember where I found those on-line. The latches are slam latches, or cooler latches (About $75 each from Allegis Corporation). The armrests are a piece of 1/2" plywood with two layers of closed cell pipe insulation, held in place with the fabric cover. All hardware is stainless, and I prefer to use nylock nuts. Here are links to a couple pictures: