I'm currently heading toward my first winter at Constitution. I bought my boat (34' O'day) last spring and have had a fantastic time at the marina and living aboard in general. I can assure you that the marina is excellent -- at least with all the summer staff. I'm afraid I can't give you much advice about living aboard in the winter because I'm reading your post in hopes of learn the same. My plan is to buy and install an espar or webasto diesel heating system -- many people here though make due with just electric heaters, but I've heard that this costs between 200-300/mo for a 38 footer. It sounds like the espar / webasto will cost in the neighborhood of $3000 for a 34' boat. A friend of mine that will be staying here this winter just bought a floor mount dickensen alaska diesel heater that he bought for about $500. He's convinced thats all he'll need. I'd go that route for price/simplicity except that I have no available floor space.
If you end up at Constitution, say hi.. I'm on Apollo.