I mill my own finish out of rough that I buy for .50/board foot. The chances of finding a completely clear 12' are rare so I will have the odd knot or 6. I've had no success with oil prime, kilz, shellac, etc. No matter what the knots will bleed through. My thought is that brushing some epoxy over the knots may have a better chance of sealing them in. Has anyone ever tried it? Of course that's assuming I can even get any epoxy. The last time I tried at the local commercial marine store they had none due Texas freeze, Mexican shut down, etc.
I'm presently trimming a barn; for any I replace on the house it's plastic, one and done.