Though I’m not 100% confident in my welding skills, I’m coming round to the idea of making the frame for the rolling roof section from a square section steel tube. I think in the end it will be lighter, less flexible and require a less complex design. It should also mean that I can have a ridged roof rather than a flat roof which I find more aesthetically pleasing. I’ve roughed something out in Sketchup, though it may change.
For holding the roof closed (so it won’t lift off) I’m tempted to use something like this:
which is actually a pin used to mount tractor implements on a three-point linkage. It could pass through a plate with a hole fixed to the walls so the roof won’t lift. When it is to be closed up for an extended period I could even use the usual spring-loaded retaining pin through the hole in the end:
Plenty more to think about before I get that far though.