This is what i use. I use it under Sig and Brodak. I have never had any problem and it is very good at filling in all the little imperfections. It sands very easy too, just give it a few days to get good and hard. I have sanded it the next day but I recommend waiting a couple.
Derek
FYI, my process is: Nitrate, (usually right out of the can without adding thinner, this will seal the wood faster and prevent excess weight) I sand it flat between coats. I apply the silkspan with Nitrate, then I move on to Sig Light Coat. After the Silkspan is on I never use a brush again, everything is sprayed out of a gun. once it is all sealed with light coat I do a filler coat (zinc powder mixed with clear). this is sanded smooth and by this time most of the orange peal should be gone. I seal that with one more light coat of Sig clear (light coat) then I spray the primer. sand the primer and you are ready for your base.
Derek