We've used both EZ-Up and Caravan side curtains with a First-Up. As long as all the zippers match, it doesn't seem to be a big deal. The First-Up is definitely superior in terms of rain risk, though, because water doesn't pool in the roof corners the way it does with the EZ-Up and Caravan construction.

BTDT about setting up for a show and then not selling anything. It sucks. At least the last time it happened I learned how to make these from one of the other vendors!