I make masters and also do some resin casting for Matador Models in the UK, this is mainly armoured fighting vehicles but I also cast aircraft hardstandings in resin for them. Number 1's description of the process is corrent, but you have to be careful handling the resin because it is not very nice if you inhale the fumes.
I just cast today a set of aircraft seats in 1/72 scale for a project that I am working on, I made the masters, produced a rubber mould using the masters and them poured the resin into it. They look OK, I wish I had more time to concentrate on this work, it is very interesting and you can make many copies of your work using the same mould dozens of times.
PV Chairman.