Well, this resin casting lark is a piece of cake - I can't see what I was ever worried about. ;)
I have started casting myself some of the APCs, but first things first. I was as careful as I could be while I removed the master from the mould, but I still managed to tear a small section. I think there was a fine gap between the hull and the plastic card base, and this allowed a small amount of rubber to get into that space. When I lifted the master out, it tore a tiny section of the mould out as well, so one of the axle stubs has a flaw beside it - indicated by the knife-blade.
Anyway, I cleaned up the mould, removing the wax and generally tidying up the edges, and then I tried a casting.
I measured the size of the void I wanted to fill, and I mixed up a little resin. A very little resin. Twenty-two grams of resin, to be precise. Fortunately I went and got a set of electronic scales from Tesco at the weekend, so I can get this accurately mixed up. I mixed, I poured, I realised that twenty-two grams may be precise, but it's precisely wrong. It's slightly shallow, but probably usable... or maybe I'll just keep it for posterity.
Anyway, since then I have cast another four APCs; twenty-six grams of resin is the correct amount to fill the mould and have just enough resin left over to make the hatch. It takes about 15-20 minutes to mix and pour the resin, wait for it to bloom and cool, remove it from the mould and clean up for another run. Not bad... and they are all small and solid enough that I don't have any problems with warping and flexing.
Final stage - attach some wheels to the hulls...
I have to say that I'm well chuffed with the way this has come out.