I just reread you reply... I definitely don't want a satin finish, I prefer clear gloss with no visible brush marks.

Are you thinning your varnish before you apply it? Most varnishes, especially the polys are way too thick in the can to use without thinning. It has to do with EPA and VOC regulations. Thinning about 10 -20% works nicely for the Behlen's RHT. It should flow out and brush marks should not be an issue.

Could be your brushing technique, could be a cheap brush. My varnish brushes are badger hair and cost $20-$60 each. Rockler carries a 2" badgerhair for ~$20 well worth it.

TIP: Pre-condition your brush... Dip your brush in mineral spirits (MS) before you start to use it; then when it's time to clean it, all your have up in the ferrul is MS. The brush will clean up like a charm. I have 20+ year old brushes that get used all the time and still look new.