Thanks @jgragg, I decided to return the 3/4" and go with 1/2", and I used a little Window & Door in the pond area before you responded. It actually hardened up for me and is a little harder to cut than the Gaps & Cracks, so I'm glad I didn't use it everywhere. But I live in a really arid environment so that might contribute.
Can you explain your process for heating and bending the egg crate? I’ve always wondered how to use that in a way that wasn’t quite so linear.
I borrowed a friend's heat gun, my boyfriend created a backdrop for me out of a cardboard box and aluminum foil (to reflect back heat, this seem to really help things heat up faster) and I applied heat along a single row of squares in 6 seconds bursts per side, until the egg crate "slumped" or seemed pliable in that spot. I think it was about 24-30 seconds total for each bend. Gently start bending with a hand on either side of the bend point, and do not use pressure if it doesn't bend easily - I shattered one piece that had cooled too much doing this. The top and bottom rungs did melt and curve a little, there didn't seem to be a way to avoid that. I did this in a mud room with a fan blowing into the garage, since it was smelly.