My wife got me this for Xmas and it has a rail mount system.
http://www.sportsunlimitedinc.com/stow-n-go-160-bbq-grill.html
Haven't had a chance to break it in yet but looking forward to it.
If you're going to use your portable gas grill on the boat cardboard to catch the drippings may not be a good idea depending on clearance and how hot the bottom of the grill gets. Or better yet, pick up a universal rail mount and bolt it up to your grill. Below are some from Iboats.
http://www.iboats.com/Force_10_Gril...7196709--**********.948858864--view_id.485108