The B36(2002) that I used to have, had the same fuel take off from the fuel tank and the same fuel filter that you have, and using one of the two fuel take off points to feed the diesel heater just as you are suggesting. The only difference being that the filter had a glass/clear plastic bowl. It worked well, and I would recommend using this rather than a second take off point from the tank in order to minimise the number of fuel filters onboard, and to keep to keep the number of different types of fuel filter to a minimum. The fuel filter you already have in place I believe is a CAV type, though I do not remember the specific model. What I do remember is that it was an absolute pain in the &#%£ to change the filter due to its location, and the number of rubber seals involved in the change almost invariably lead to minor leakage occurring from one or other.