Thanks for the message Jason.
I actually did some thing similar to what timmyboy76 suggested and it seems to have helped.
I am only heating with the hotfox. I have an additional fuel pump on the engine side of the valves. Separate filters for VO and diesel. So fuel goes through filter before fuel pump. I was going through filters every 1000km. However not because they were dirty. I filter down to 1 micron. Just the act of changing them seemed to release the air lock in the system.
The system was installed by plantdrive.ca Which I do not recommend by the way.
The vented cap I have is similar to what you suggested. However, it seems to be constantly bunged up by VO.
Fuel lines are 3/8 high heat hose.
I have tried a variety of filters with the same result. Ramco, FRAM, Luberfilter. Water separating and not.