I was going to buy an isolater but when I went to a custom audio place they just said they would rig something like that (in other words they didn't have a clue what I was talking about).
The remote starter is actually pretty easy to do as long as you take your time and get the connections right. I actually thought it was fun. Showed it off to some friends and I'll be putting one in a friend's chevy and making a race style start system for a friend's car.
...yeah we get pretty harsh winters over here too. I remember three times where the temperatures were in the 20's.