Sven, I built a wood door frame and door that is also covered in shrink wrap. I removed the aft section of lifelines so we step directly into the cockpit.
Our heater is a Hurricane H2 hydronic. I did a lot of research and found them to have a reliable well designed heater. Their support is also great. But they are one of the more expensive heaters. So far we have been very happy with it. Here is a link to my installation: