as long as the boat cover is tied down tight I rarely have a problem with one falling over and if one does it's no big deal to prop it up again. Also, I'm in southern Calif where we only get nasty weather a few times during our "winter".
The problem with poles is they tend to fall over with wind or weight of water. I used 2" ABS to hold the poles and toilet closet flanges as bases glued into a few feet of the 2" ABS. Cheap $$$. Never thought of using Frisbees on top, great idea. Mine fit snug into grommets in the cover.