Okay, before anyone gets upset, my dog doesn't stay outside at all times... Sometimes when I leave for work my Golden Retriever just doesn't want to come back inside and he chooses to spend his day outside. (I have a fence up for him) Now, he's about 11 years old and his current house needs some repairs. With winter coming, I have decided to just buy a new house. However, I am confused as to whether to buy a wood house or a plastic house. I have seen both houses with insulation. I must have insulation if he is to be outside when I'm not there because I won't be able to let him in until I get home from work if he decides to stay out. Anyway, which would be best? Also, what's the safest way to heat it? Last year I bought these little discs that you heat in the microwave and put in their house and they seemd to work ok, but were cold by the time I got home. I just want something that will definately keep him warm until I get home becuase he's starting to get arthritis. If I can't keep him warm, he'll just have to stay inside all day and I know he'd much rather play outisde and chase the cats... Any suggestions would be greatly appreciated.