Hard...I see nothing wrong conceptually with hanging 80 pounds off the back of the boat...but i would be concerned about the structural integrity of the C30 transom in heavier seas with something like that. I suggest that you visit some of the C30 owners group forums or write to Catalina directly to understand how to do this so that it is structurally sound.
Personally, I think it will detract from the look of the boat and the re-sale value and you can accomplish the same purpose by simply lashing the dink to the boat and driving it if the main engine fails.
No longer posting. Reach me by PM!