Thanks for the comments and advice.
Mike, sanding the primer, I didn't even think of something like that. Thanks.
Undertow, I have not had success hiding seems with any other method. This was clearly the best method I have tried. I used bondo when building my super v cabinets. I would use epoxy over bondo any day. I also feel like my next epoxy project (stands and wedges) will be easier simply because of experience. So Mike's advice about a practice box makes total sense, and really valuable.
Wired them both up and tested them last night, everything went fine. Now to decide on stand design. Something sand filled, or similar.