2 sided sub

Being new to dye-sub we are just about to try 2-sided keyrings after some small successes with mugs, metals and plaque boards. When doing 2 sided sublimation do you press one side at a time...or both sides simultaneously? What's the best way to protect the finished side while doing the second side..if this is 2 step process? Thanks for any and all tips and suggestions:)

I don't know of a way to press both sides at once. I would just be sure the top and bottom were covered with paper to prevent blowout but it seems pretty straight forward.

T-shirts are another matter.