I dunno Herzel... The VACUUM at speed really...
SUCKS at the roofs... and when I used an inexpensive canvas for my Bimini Prototype top... after ONE 60 mph jaunt it left it stretched out and limp. (Wetting it shrunk it to be too small afterwards too...)
(This one was affixed using the front and rear sections of a standard top and side bars holding the glued on canvas over the entire top taunt. Essentially, it was a conventional top with the center section missing so it could be folded up and placed in the rear trunk.)
My point being... I can't imagine a magnet strong enough that would hold the top in place that I could/would feel confident about... but I sure don't know much about the ones you speak of. They sound so strong that they would probably suck the paint off the car when you went to remove the top.
Knowing that you have had trouble in the past due to your stature and position in life...
(Herzel pictured second from the left...) I think I would have someone in your area build a top like the prototype that I attempted. A sourced top as a donor for the front and rear latches... and then some
strong "scissor-like" arms on either side to stretch and hold them apart with a GOOD convertible top material glued and secured down over it would probably be the best for you. Light, strong, portable, and stores in the rear trunk leaving your 'dual-shock' opening front trunk a wide open void for your groceries!
Jimmy D made a simple drawing of what I mean...
My only change would be to use scissor supports on each side that are FIXED as I found that straight supports such as these could not easily be latched and then stay
inflexible as well. I think the scissor supports I mentioned can be found at hardware stores for supporting legs on tables and such... or an old (or new?) table could be a donor.
Have fun!