1) My $60.00 Snowplow Doors.
Ebay: Adhesive backed rare earth magnets - the adhesive holds them in place while the hem is then glued around them with 3m 80. Boat window vinyl and 2 yds of Waterproof (yeah, we'll see...) Cordura (backpack material), all from Ebay.
Northern Tool - 3 Driveway fiberglass wands - 2 cut down to fit in each side as a 'hinge'; I dropped a 7/8" chair leg 'bumper' (Home Depot) down into a little rectangular recess in the frame, fits perfect and holds the wand steady, with just outward pressure against the frame on top. Cut the 3rd into a couple pieces for an insert in the front hem for a bit of a 'handle' to snug up the magnets to the roll cage (See window-less inside driver door pic).
'Dual Locker' Velcro clone from my hunting buddy nephew Mark, a can of 3m 80 Vinyl and Rubber Spray, and a ton of help from Mark and Braden. Velcro in back / top around the outside of the rollcage to the 'hinge', and on the inside of the door, and then magnets on the front to hold the front of the door into the inside of the rollcage, but allow for quick and EZ in/out. Holds up at top speed.
I started with a cardboard template, cut real big, and still goofed up a couple spots on the first door (passenger, see pic). I had to glue some pieces on to have coverage. Second door went much better - I knew I'd mess up the first one so did the passenger side first.. I used Sho Goo (zip tied til dry) to back up some of the Dual Locker, which is backed by a sticky adhesive like autos have on the body badges, and that got a little weak from re-positioning a couple times. Will need to 'peel off ' doors when necessary by carefully by holding the Dual Locker, not just grabbing the material and pulling. It's holding up well, and the velcro section will be a once per end of season removal - magnet work great for the actual 'doorway'. Hinges may not be required, but it was fun engineering them.
The windows are tricky. I did it in 2 steps, first gluing the window to the Cordura - requiring some sloppy masking and blocking - then gluing on a reinforcement border to assure it held well. I still have material for 2 more windows so can replace, but they should last for years.
2) Rocketbox for backcountry crew transport - Didn't need it for archery elk this year, but just re-purposed roof rack bars from various vehicles to mount the rocketbox in case we needed to shuttle back in there. Intended area was closed (SW MT, Gravelly range) due to bears feeding on cattle carcasses. This would have allowed 4 bows in cases and all our campgear to be staged in farther from the road.
3) Golf Cart rear seat flips down for cargo - on sale - put the skinny guys back there...