This is a response from an Electricians Contractor forum.
Yes, that would work. But I wouldn't recommend it. GFCI's are very sensitive, and if the cumulative ground leakage of everything connected to the subpanel reaches 5mA, it will trip. It would be better to put a GFCI breaker in the subpanel to supply only the brewing equipment. That way the amount of equipment connected to the GFCI is lower, and the breaker is right there so it's convenient to reset if it trips.
So I'm no longer considering the QO240GFI breaker in the Basement.
Considering the Spa Panel
or maybe a 40a SP Breaker in the Sub Panel. Would need to know how to make GFCI on this setup.
or the HOM220GFI breaker in the Sub Panel Probably the cleanest setup. but pricier.