How to smooth out the Progasm ICE?

I would concur that this seam (the molding line) is very small, but if you feel the need to deal with it, you will have to do some progressive sanding. Start with a wet/dry sandpaper 320-400 grit to work the seam down and then switch to 1000 and 2000 grit sandpapers for smoothing. The latter two products are normally available for clear coat sanding for automotive finishes. This sanding can be done dry or with water. Why water? It keeps the paper from getting clogged up with particles of plastic. Be advised that you may not get the finish of the ICE back to the way that it looked prior to the sanding, i.e. it may look a little dull in the areas that you've sanded.

Good luck

BF Mayfield

No experience with the ICE but a bit of toothpaste on a soft cloth works on some clear plastics. Goggle for a 'jeweler's rouge cloth' -- also a winner for final finishing.