Lee valley sells rare earth magnets quite reasonably.
Lee Valley Tools - Woodworking Tools, Gardening Tools, Hardware
They have a starter kit with an assortment or you can order them one at a time in most sizes.
Depending on the way you attach the skirts they will probably work very well. I think if the wind can't get under your mod to pry it off you are o.k.
I use them for attaching one of those $1.49 foil blankets from a camping store when I park in the sun. It's almost as good as parking in the shade and the magnets are almost invisible on the silver plastic. The long magnets work best because you can get a grip on them. The flat ones are hard to pull off.
Another way for quick detach is dzus fasteners which were invented for aircraft panel quick release. The are spring loaded, flush and can be installed with rivets or screws. Also used in auto racing, etc.
Self-Ejecting Fasteners
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