I'm tellin' ya bro, try the mirror. You don't lose one bit, it's all easily scraped up with a razor. Besides, the chance of getting any bits of cardboard in the bubble sucks.
I also froze mine, but I need to explain: When I was making bubble, I used a DIY bubble bucket set. That allowed me to take the screen off with the bubble still in it (the 73u was normally the best screen for the strains I ran at the time). I collected all the bubble into a corner, dabbed the majority of the moisture off with a towel, and put the folded screen into the freezer. After about 10 minutes, I'd pull out the screen, carefully unfold it, and pop the frozen hash off onto a mirror.
A touch bit of moisture actually helped to get the hash off all in one frozen piece, so long as I collected all the trichs together well in a corner. (I would fold the screen in a certain way, that would allow most of them to pool together nicely. Any stragglers would be gently moved towards the pile with a water squirt bottle.)
Bud's DGS Grow
I don't start it, I finish it. Remember that before you get disrespectful. If ya wouldn't say it in person, don't say it online. Some of you were obviously never taught the Golden Rule, google it!