The unit works in the car, and the adapter doesn't smoke. That's good news. It means that most likely there is a big surge as it turns on (as suggested by MikeD), or the socket in the Winegard deforms when you plug it in, and something shorts. I am a little surprised by either possibility, but I don't see any others.
I don't think the cig lighter in the car is fused at any more than 15 amps, so the fact that it pops a 15-amp fuse in the Winegard makes me think the Winegard is bad. To test this theory, do you have (or would you like to get) one of the 2-to-1 cig plug adapters such as
http://www.campingworld.com/browse/s...26776&src=SRQB or
http://www.campingworld.com and type 26776 into the Search box.
It is my experience that some 12-volt plugs are slightly oversize, and the Winegard is not particularly tolerant of an oversize plug. If you plug a 2:1 adapter into the Winegard, and then plug your TV into one of the adapter's outlets, and if everything is then OK, then the problem is in the Winegard.
If the problem turns out NOT to be the Winegard, then you might try a Slo-Blo (slow blow) fuse. It will hold against a substantial overcurrent for several seconds, but if the overcurrent continues, it will pop. You should not change the basic rating of the fuse, though - change it to a Slo-Blo, but keep it at the original rating.
Bill