I think if you follow the instructions it should be okay to iron - some waterproof clothes are ironed after washing to re-activate the waterproofing (not sure why but I read it on Didrikson technical info page). The zip can be opened at either end, so might be tricky until you get used to it - my haven is 3 years old now and I haven't had any significant bother with the zip. Make sure both zips are together at the bottom, hold the bottom part with one hand pull the upper zip part upwards to zip it up. Hope that makes sense. I just tried doing it and it seems fine.
That's an interesting tip about the ironing Tapsel, I had no idea! Presumably you should put something like a tea towel between the coat and the iron though, and I definitely wouldn't do it too hot...
Also interesting about the zip, I have exactly the same problem with my Didriksons coat. I thought at first it might be faulty but I'm getting the knack of it now. With mine, I've realised that the trick is to hold the top parts of both zippers firmly together with one hand to make sure that they're perfectly aligned before even trying to insert the "male" piece if that makes sense.
Am working up the courage to wield the iron now to get rid of the creases, and also panicking a bit that it will be warm enough as it doesn't feel as thick as I thought it would. Just want to be warm this winter for a change!
The first winter I wore my Merrell Haven I felt like I had put on an electric blanket. I have poor circulation, often feel cold in the Scottish summer. I am in the NE Scotland, have had some horrendous winters here, one mile to school on foot, 30 minute wait in the playground outside, between dc1 finishing school and dc2 finishing school, temperature below or around freezing for months. The worst day was one afternoon, freezing fog, and it was -13 in the playground, it dropped another two degrees on the walk home. I was cold in my Merrell that day, but I think I needed better boots and other layers (was wearing thermals) if I hadn't been wearing my Merrell I would have been beyond miserable!
I would probably use a tea towel or muslin when ironing, just to be safe.