Hi Steve; There are probably as many ways to put finish on a rod as their are rod makers. Whether you brush, wipe, dip, drain, pour, or spray, good results depends on knowing how your particular varnish behaves. The best way to find out is practice with some inexpensive 1/4" wood dowels. Try what ever method you pick on the dowels before making a mess on the blank.

As for thinner, I would use the best grade of pure turpentine I could get. I have had problems with mineral spirits and paint thinners making the varnish gummy pretty quickly. The generic name mineral spirits covers a lot of ground and could contain all kinds of stuff.

Best of luck with the project.