G,Day Tommahawk
Mate you can get extruded alluminium section of different types fairly cheap and rectangle section tube . Top frame is just 2" x 1" ally rectangle box section screwed / riveted bolted through the roof sheeting then either do a DIY job and make the canvas / vinyl tent sock yourself or get an upholsterer to sew you one up ..These tutorials might help if you DIY .
https://www.youtube.com/results?search_query=sailrite+videos...
Bottom Ally extrusion is aprox 1" x 1" square with a 1" tag off one side [ other sizes available ] sealed and screwed / riveted / bolted to or through the body tub walls .
Drawing is of how I have done canvas / vinyl walls on campers before..
Black is the ally sections
Green is the canvas / vinyl [ rolled around a 1/2" x 1/8 th ally flat bar ] seal to ally section with Sikaflex sealant
Blue arrows are Screws or mushroom head rivets to hold the canvas etc to the ally frame
Yellow / orange is roof sheeting and body tub respectfully