If you are making outdoor items and they get wet a lot, they are going to eventually rot. Putting on a coating will extend the life marginally, but is not worth the trouble and expense in my experience. Most large bamboo that is cured is dried over a period of several days in a big, smoky, outdoor oven: this reduces moisture content and kills any bugs. In order to minimize splitting, it's common to also take a piece of rebar with a pointed end and ram it through the bamboo lengthwise to break through the nodes. If you don't want to build a giant oven, you can air dry it in a protected location.

Thanks for the answer Kudzu9!

After coring it I use a old woodstove with a 4" flu inside a 12"flu(open at both ends) to heat dry bamboo but you have to be carefull not to burn it. I then use a pvc pipe mostly full of laquer to soak it before I use it. It's not really economical for most uses but I do this before refilling to make fishing poles. My buddy uses mineral oil and it works great but needs to be periodically reapplied.