If you want to be sure your nylon screws break, make sure you have them going into metal mounts. The mounts can be hard mounted to the structure and protrude through the deck or soft mounted to the deck using under deck threaded inserts or threaded metal plates with nylon screws, just like the uprights.
Just had a thought. You could use ferrous metals to make the mounts and have them held on with modern "supermagnets" installed in the deck. Conversely, you could use magnets installed in the deck and hard mount a ferrous metal strip in the bottom of the uprights. It would do the same thing as the nylon screws but it would also eliminate the need for them and the possible damage they could cause if hit
