Re: Bamboo hobo dapping rod build advice - some photos.
Varnish would not be my first choice,
I would cure the bamboo for a good long while before making a pole from it. Once I had a big dry clume I would wrap it with a cotton cloth for the entire length and apply pure linseed oil to soak the cloth. Then I'd wrap the cloth with regular plastic or 3M tape and drape painters plastic to keep it wet. After 24 hours of the oil bath wipe the cane of any excess linseed oil. Then hang it so as not to promote a 'set' and let the oil dry for another week or so. At this point you are ready for hand rubbing to finish the process and it's time for the line guides and wrapping.
I have stripped and refinished old varnished cane rod blanks and when they were ready soaked them in a PVC tube filled with linseed oil. I then dried them for a week in a temp controlled environment before hand rubbing the finish. The rods all fished great and the oil impregnation looks very nice as a finish.