Having built and renovated more rods than I care to remember, the problem of what to put on the whippings is the biggest headache. In the past I have used ordinary varnish (back in the 60's/70's) various 2-part epoxies, a single pot, water-based stuff that Steve Parton used to sell, but now I only use Flex-Coat which is a 2-part epoxy and, as the name suggests, is flexible.
My favourite whipping colour is Gudebrod claret, undoped, so that it goes a deeper shade with the coating. if you try to get a perfect, teardrop, professional finish in one coat you will invariably fail. I put a first coat on, most of which soaks into the whippings. When this is hardened take a scalpel and nick off all the little spiky bits that may have appeared where fibres have protruded or any little air bubbles that appeared and didn't vanish of their own accord. Then apply a second, more liberal coat, and observe the usual tedious turning of the rod until the coating no longer slumps and Bob's your uncle.
An upturned shoe box with v-shaped notches cut into either end is usually good enough to hold the rod during the turning process.
