I used to own a TJ and I had my XM sat radio antenna on the roll bar, under the padding. it fit in there fine and it worked great.
I don't have my jeep anymore, but I DO use a Globalsat BU-353 antenna and I can tell you it's almost the exact same size as my XM antenna. I can't imagine any problem at all fitting it under the padding. if it really was a tight fit then you could always cut out some padding (you won't see it because it will still have the nylon cover over it)
I know first hand that the BU-353 works great so I can highly recommend it
good luck with your carPC
