I use a small sable brush with 50% thinned spar. Build it up to where you want it. I then use the turkey baster type method to coat the complete rod-I've cut the spar with artists grade turp, naptha, and mineral spirits 50/50, put it in a small bottle (plastic ketchup or mustard bottles from the store works too)
Wipe the rod down with a tack rag and line a paint tray with foil. I do this in the shower stall, with a bar over head to hang the rod pieces from. I wrap the ferrules with teflon pipe tape and drizzle the spar slowly down the rod, turning it as I go. Do each section like this and hang it to dry. The excess varnish runs into the paint pan and I reuse it. I usually wet down the shower to take out any dust. Wash your hands and arms good and don't wear anything fuzzy on your arms. A couple coats and then decide if you want another coat after that. Let it dry 24+ hours between coats. I've done it to several fiberglass rods I've built and they come out nice. If you pick up a piece of dust, after it's dry, wet sand it out and wipe it down with the tack rag and give it another coat. Don't worry about the spar getting on the guides. I wipe the tip top off with thinner when I'm done.
Use spar with UV protectant in it.
Rockthief and Lotech have seen pictures of my rods.