the areal antenna base has corroded on my mk4

[mcgee9t2]

anyone used one of these?
http://www.ebay.co.uk/itm/Universal-AM-FM-Radio-Hidden-Windshield-Mount-Camper-Car-Antenna-/310355201468?_trksid=p5197.m7&_trkparms=algo%3DLVI%26itu%3DUCI%26otn%3D5%26po%3DLVI%26ps%3D63%26clkid%3D5234605987790928041
cause i dont fancy paying 70 quid from the deelers.
also any ideas of what i could do to plug the hole in my roof?