As always, Thanks for your thoughts and preferances.
I am leaning toward using the gen tank now.
I like this idea.
I agree with Brian -- pipe the Webatso supply and return to the separate generator tank. You can then use off-road (dyed) diesel in that tank, saving some money on your heating.
I would also install a small electric fuel pump and a manual, moentary switch to transfer fuel from the main engine tank to the generator/webasto tank. This will allow you to get some fuel to your generator and/or Webasto in an emergency.