I do a suck down with Copyplast from great lakes. I use Light cures triad to hold the 3-3 on while I thermoform. After thermoforming i take it off, hopefully I had captured enough undercuts on the 3-3 that it stays in. then I take the 3-3 out of the copyplast, use some scissors to cut out the shape I want, and clean the triad off the 3-3.
As far as packaging. I put the 3-3 back into the copyplast matrix and put it back on the model. then I put the model into a baggie and heat seat it where the model it pretty snug in the baggie where the matrix won't come off in shipping