I have one of those indoor safe Mr Heater boxes on my boat and absolutely love it. It puts off enough heat (6000 BTU max) to keep the Misses warm, so I can do the fishin' and she does the drivin'.

My boat has the Alaska bulkhead, so we're using it "indoors". Of course, you have to be safe and appropriately cautious, but I think the Mr Heater folks are going a little overboard (pardon the pun).

Considering our lawsuit-happy society, they would be foolish to officially support using a propane heater in any type of contained space. I bet they would even consider it unsafe to use these heaters in your garage. Actually, you're not ever suppose to bring a propane cylinder indoors.

Obviously, it's your call, but I'd say get the heater and enjoy cold weather fishing.