Failure to use a sanding sealer on bare wood prior to painting guarantees two things.

#1- The wood will absorb a lot more paint than it needs to provide the finish, making it a lot heavier that it need to be, and

#2- Obtaining a smooth finish in the paint will be next to impossible unless you build up a 1/16" layer of paint that can be sanded down to eliminate the wood grain and other imperfections.

Short answer is yes, a sealer should first be used.

In the old days we mixed talcum powder with clear dope to make our own sealer, but I don't know if your choice of finish and dope will be compatible.