I came up with this idea I saw on Apogee, except it was used for making motor mounts stronger and lighter, which I have used and it does work. I covered the build process under my GFORCE build thread. It consist of a wood dowel, some card stock and wood glue to put it together. You cut a couple rings and space them however you want on the wood dowel and then use the tabs to reinforce the rings. The rings are cut to whatever diameter rocket you are painting. This allows you to hold the rocket and paint without getting paint all over you or you can stand it up or what I do is wedge it in an old plastic milk container you find behind supermarkets. I have several that I made over the years and still have them. You can take it a step further and make the whole unit out of wood and disregard the tabs for support, although the wood units would work well for the really big rockets.
The unit pictured is for a 4 diameter rocket.
The unit pictured is for a 4 diameter rocket.