When I first looked into the RLC it was because I was a life long Republican who developed a libertarian view. I remember at one time the RLC saying it was made up of libertarians who saw the Republican party as the best tool for spreading their philosophy, and for seeing it enacted. I agree with this.
The third party route is a sure fire route to political obscurity. Within the GOP is the best route for these principles to be spread. The important thing is the spread of the principles, but the need for majorities to accomplish an agenda makes alliances with a major party necessary.
A third party would ensure the win of our opponents and the shelving of our agenda. If you are willing to shelve the agenda to claim the moral high-ground then go ahead, but don't be surprised when you get nothing done.
I wonder if the DFC would be willing to vote with the RLC on bills...