I made an advent calendar from a panel piece. How would you suggest putting some batting in between the front and back piece? thank you.

Can you post a picture so we can see how it's constructed?

If the pockets are already on, I would fuse some batting to a piece of heavy non-woven interfacing and sandwich it between the panel and backing fabric to quilt it. (batt toward the panel side)

The interfacing will keep the panel squared and flat while it's hanging on the wall.

You might have to quilt in between the pockets or at least sew around the pockets to keep them from sagging, especially if you put candy in them.

Hope you'll show pictures when you're done. :)

i would say that quilting/sewing between the pockets is a must. however, a pic would be helpful