In a message dated 1/29/2015 1:43:57 A.M. Eastern Standard Time,  
jpalmer@mymts.net writes:

I’m  confused.  Is the Webasto BBW46 for heating the cabin or heating the  
coolant?  
Jeff
85 Westfalia with cabin gas  heater

preheating heating the coolant which in turn gives you instant heat in the  
cabin.