I'm not seeing the sketch but I don't believe it would take much just an orthogonal set of rollers, maybe just 3, that are lightly spring loaded to keep it in place. Are you going to just move it by hand or are you looking to use motor control? Reason I ask beyond just curiosity is I currently have a 10' HomeDome. The mechanical configuration and mechanism that rotates my dome, IMHO, is a Rube Goldburg. It continually fails, is not very robust for temperature changes between seasons and basically is a major PITA. I'm looking at replacing it with a rack/pinion setup. Can't do anything at the moment as it's way to cold where my observatory is at the moment but come the summer I'm looking at reconfiguring it completely and I'm interested in what approaches others are using to solve the problem.
Nice you have experience in working with fiberglass. That stuff can be particularly nasty but if you know how to work with it you can get some very nice results. Looking forward to more pictures and the progress on your build.