I'm thinking this is a stupid question, but I will ask it anyway. Is there any reason not to use a Bowden cable clamp (like http://www.aircraftspruce.com/catalog/appages/bowdenclamp.php) for routing the heater and alternate air cables through the firewall? It seems an obvious application, but I can't find any posts alluding to this or any photos showing anyone doing this. Makes me wonder!