how bad is it bro
if i would have to quess its nothing that i would worry about
imo there is almost no way that the water soaked the wood all the way thru enough to worry about scraping out the stand
if the overflow was stopped up by your mag float then the water was overflowing the tank by the pump
that means that water was standing on your stand
that would then leak down to the underside of the top peice of plywood
just let it dry out
it would take alot to make that plywood rot enough to fall in
throw some fans on it and don't worry about it
mike