/cgl/ - Cosplay & EGL

Hey gulls, sorry if this is a stupid noob question but I feel like a complete idiot right now. I decided to try these bases everyone is using now and taped it with clear mailing tape and thought I had sealed it and everything, but apparently I'm dealing with mold leakage. I'm using epoxy resin and I know most people use UV for these so is it just that epoxy eats the tape or something? Do I have shitty tape or molds or resin or am I just a dumbass? What am I doing wrong?

Luckily I noticed and could save it by peeling off the excess resin around the sides while it was halfway hardened, but I'd like to not have to peel off a mess every time. Pic as example.