I would use, and have used, Lifseal. 4200/5200 will actually flex plenty enough for this application, but they are more of an adhesive than a sealant. They'll seal just fine but as Seasick mentioned, will make removal much harder.
Sand the wood core to expose fresh wood and then saturate that a few times - just keeping going till the wood stays shiny after about 10 minutes - with epoxy. Watch for drips/heavy spots on the bottom of the hole and sop them up before they dry so you don't have to come back and grind them away to get the tube to fit. Once dry, give it a very light sanding with some water and dry it. Then use your Lifeseal (or whatever) and fully coat the hole with your finger before doing your final sealing/installing.
Personally.. I like using the 2-piece plastic ones from TH Marine. Brass doesn't last forever, either, in this application and the plastic ones are much easier to install/remove.