[Arran]

Actually removing the glue gun glue is pretty easy, I've remelted it with a heat gun on occasion to make adjustments to the leads or to tidy up the ends. The melting temperature is lower then the hard wax the manufacturers originally used to plug the ends, it can also be cleaned up with lacquer thinner.
The cardboard I have been using is a sort of thin corrugated type used to package China ornaments for the stores. It has two or three layers and you can peel off a layer to make it thinner. I cut the strips so they are slightly wider then the body of the new capacitor, then I tack it one end of the strip onto the body of the capacitor and wrap it around the circumference.
I guess you could also use wax for filler, but finding anything other then paraffin candle wax around here is a problem. I don't like paraffin because the melting point is too low.
By the way, I test each capacitor on an EICO capacitor tester before and after I stuff it into the old tubes, just to make sure I don't have to pull it out again.
Regards
Arran