If you've already got the RUE-M1RF kit, and you'd like to add an additional remote, the RUE-M1EX is the one you're looking for.
Price: U.S. $60.00
Professional installation available at authorized retailers.
Previous remotes mostly used infrared (IR) designs, which made them poorly suited for the outdoor boating environment because sun reflection interferes with the IR remote eye. The new Alpine marine remote system uses RF (radio frequency) technology to avoid this problem. Now you can control your system with the remote from up to 100 feet away!
For use with the RUE-M1RF remote system. Program up to eight remote controls on your boat.