I've installed several small TV antennas on boats - West Marine among others carry them. They are roughly a 10" round plate atop a 5 or 6 " mount. You could probably even get a removable mount and fix a coax plug-in on the side or bottom of the tear so that you only mount the antenna when you are using it and stow it inside the cabin other times.
Steve, I just checked out West Marine's site and there are 3 models listed but they seem to be a bit larger than I remember - about 24" round. Found a 14" model on http://www.boatersworld.com that is closer to what I've used in the past. I think it's around $130 - nothing about a boat is cheap...
I checked at West and too expensive. The cheapest they had was $159 and they were amplifed requiring power. I'll probably get a set of rabbit ears and make a base and a lead with a connector and just put them on the tear when camping.
I've just been using the single pull out antenna on the back of the set and it works, but very poorly inside the aluminum box which is a pretty effective RF shield.
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I bought one of these to pickup HD signals (for the living room TV). It doesn't work all that great. It is very directional, I can pickup Belton and Waco stations easier than Austin stations. I can pick up the Austin stations but I have to aim it at them, then it falls off my entertainment center.
The antenna that has been getting good is called the Silver Sensor. It is pretty small albeit a bit finky looking.