drive the hartop instead! I would try Scotch guard, but it you should try it in an inconspicuous spot first. my top has gotten wet before but its a hartz type top and it repels ok, but I have not gotten the full drench yet. I usually just run my convertible in the summer
They make a Scotchguard style product to waterproof and protect boat bimini tops. Id look into something like that.
Here is a spray recommended by Hartz for waterproofing their canvas. https://www.worlduph.com/others/convertible_top_care/