Not sure yet. Either like you did or sealed with a port.
I already built one as a test run with cheap materials from walmart and insul from joanns, so I know exactly the shape and foot box I want.
Just out of curiosity, has anyone played around with a semi inflatable quilt ?? I am sure its been done somewhere in the world. Sort of like a exped synthetic synmat where each side would be bonded. You could do it if you glued the edges, otherwise the seams would need to be on the outside. If I was going to put a port in anyway it would make sense. Seems like it might be a little warmer for the weight and size.
Not sure it would be worth all the trouble, and it would be a lot of gluing.