For those interested, and maybe even for Sebastian747, I just bought this from Andy, and in the process of reading the build diary, realised that the polishing solution (that is the problem of keeping it looking good, rather than the rubbing down) was sitting in front of me. It's called Greygate Plastic Polish, and was designed with Plexiglass/Lucite aircraft canopies and similar in mind. Smells a bit iffy, but will actually work well on most plastics. There's even a specially formulated version for nitrocellulose plastics also.
The catch? Tends to be only available from aerospace suppliers! However, if I can find such in Okehampton, it can't be that difficult elsewhere, I'm sure!