Installation -

1. Create a "RoamingTrader.sqf" and place it in your mission file

2. Either create, or add to your "init.sqf" this - [] execVM "RoamingTrader.sqf";

Inside RoamingTrader.sqf paste this code -

http://pastebin.com/LjwNpZCg- Latest version written by me includes option for trader in vehicle also has options for randomizing the trader type.