CD relay is a continuous duty relay. S605 relay works. Cole Hersee has spst CD relay in varying ratings. Make sure it's sized properly.

http://www.colehersee.com/home/grid/cat/169/

See the diagram linked above, not the first post, down a few. On a street car, instead of triggering the CD relay using the cut off switch downstream side, use a keyed source. That way the CD relay only active when the car is running or key on.