I still say ditch the nuts and bolts, and just weigh out how much modeling clay you need with the washers and use that.. If you use JB Weld or an epoxy, you're stuck with that tuning forever.. With clay, the washers really wont go anywhere, and you'll still be able to play with the tuning in the future, if needed..
The method used for mine is as follows:
Squish some clay into a thin slab about as big around as the cardboard tube, and smoosh it down in the bottom.. Add a washer on top of it and squish it into the clay.. Then another thin slab of clay on top of that, smooshed over the washer.. Then another washer, more clay, etc, and top it off with a last slab of clay..
It really won't fall out.. The clay is plenty sticky enough to hold itself and the washers in without any movement..
Epoxy if you really want to, but down the road you might regret it..
Travis has the right idea. Part of the fun of a PR system is the ease of changing its tuning frequency when you feel like experimenting. I used that poster-tack stuff and washers in a way pretty similar to what Travis described. If you get it wedged into the tube pretty well it won't come out, but it'll be pretty easy to either add or remove mass later on.
I think you guys might be misunderstanding his intentions. The reason to use the bolt and washers, and then a nut is that you can pop your PR's out, take the nut off and slip a few washers on or off, put the bolt back on, and away you go. To me this would be far more elegant than modeling clay.
What I did was cut out an MDF disc just slightly smaller than the tube on the back side of the PR, and then basically countersink the bolt through the back side of the MDF disc, and use some epoxy to keep in it. I then expoxied the disc assembly into the center of the PR tube, and then put the number of washers on.
You do need to weigh the disc/bolt combo to know what your starting weight is without washers. I suppose this isn't necessary with the clay method.