oxford said:I belive that there is also a product called lab metal that can also be used. It is probably best though to ask the coater that you will be using for what he recomends.
You should also leave the filler slightly high and then have the tank put in the oven at the temp the powder will cure at. You can then final sand after this. The filler may shrink some with the heat and this will make sure you don't have any low spots in the finished product.