This is just a suggestion that you might try. I have had very good luck with marine epoxy. I would rough up the hole slightly install the plugs smothered in epoxy. After everything is set up you reach into the hull and put hose clamps around each of the posts that stick down inside the hull and tighten them up (not too tight). The trick is to apply the pressure to the now solid epoxy joint after everything has setup, in this case the epoxy is forming a more solid plug, the hose clamps are what hold it in (the epoxy of course doesn't stick to the PE hull).
Here is another method that will work also. If you go to any art supply place (or some Home depot's) and pick up some Bestine solvent and thinner (you can get it online here ( http://www.amazon.com/RUBBER-CEMENT-THI ... 382&sr=8-2
) at Amazon.
This is almost pure Heptane (which softens polyethylene). Take a cotton ball and stuff it into the hole then soak it with the heptane, let it soak in for a while keeping it wet (maybe 10-15 minutes). You then coat the outside of the plug with cyanoacrylate glue, remove the cotton ball then shove in the plug (quickly and don't stop halfway down). Once it sets up (almost instantly) you will have to drill it out to remove it. If it were me I would put the hose clamp around the post also for good measure.
You can get the same stuff from Locktite called Loctite plastic bond ( http://www.loctiteproducts.com/p/sg_pls ... System.htm
) at home depot (but its ten times the cost). The whole trick on bonding PE is to keep the heptane (which is thin like ether) on the surface as long as possible, so on a lap joint you would soak a rag put in between the joints (keeping it wet) let it soak a while, then remove and bond with the super glue, you won't be able to get it a part. Try it on some scrap injection molded PE (not milk cartons, that's a different type (HDPE)).
Sorry for the long response, but just about every other thread someone has problems with adhesives on their plastic hull.