Is that a 30 inch J mount or a 30 foot J mount?? Really the best to do at this point is what the other question askers do -->
http://forum.tvfool.com/showthread.php?t=4 . With the radar report , use your exact address and inter in the antenna height. So we can have a look at your reception situation. It helps use learn more about reception conditions every where. Any way , what can be done is get a pipe that will fit the inside or outside of the J mount pipe and drill a hole all the way through both pipes and put a bolt through.