Hi!
Why use 30min epoxy??? I use thin Ca glue for this...if I ever bother to seal the tank area at all... Most of the time I don't bother.
Finishing resin epoxy is good though much better than ordinary glue epoxy that has to be warmed with a airgun or thinned with a little methanol (not too much and the epoxy gets rubbery). Better is 2 part car or boat acrylic or polyuethane lacquer (Sikkens or PPG).

Regards!
Jan K
Sweden