15-20 miles is certainly possible.  It will work better if you have Glonass enabled.  You may not have sub inch accuracy, but you can spray and side dress in 30" rows at that distance.  We do it all the time here.  You just need your 442 setup to broadcast the correction data to an IP address.  The 442 has an ethernet port, but I think it will have to be connected to a computer to act as a server.  Intime can get you going and I think there are other products on the market that can to it as well.