Another look at the mould making stages:
1. The rubber has set after the top (first) pour.
2. I've inverted the boxes and detached the bases, and rather obligingly, although the cabs were glued down (no raising of the Titanic unexpectedly this time) the glue has given way just where I hoped it would, releasing the bases cleanly from the undamaged, undisturbed cabs. The "keying" pips and strips have also been left behind in the rubber. This illustrates how invasive the rubber is, creeping into any slight gap in a glued joint and tending to pull that joint apart if "tested". This time I've benefitted from the effect. Quite a layer of rubber had managed to sneak under the rear edges of the V-front cab, rising inside and compressing the trapped air to some extent. Thankfully, the master bodywork itself does seem to have been fully sealed by my efforts, so no rubber has crept through in really awkward places.
3. Closer view of the opened base. I've dug the key strips out of the rubber to open up the impressions for the second rubber pour.
4. The unwanted ragged tongues of rubber have been torn and trimmed away to leave a clean face.
The next stage:
I've built an extra new layer of bricks around the edges of the box and added provision for some large tubular feeds (with conical mouths) to take poured resin down to the depths of the closed mould (once it's made) and some finer breather airways to let air out of the top as the resin level rises. The long mould will be slightly tilted as I fill it to drive air progressively from the deep end first and towards / out of the high end. I hope this will more easily and effectively drive out all air bubbles than my earlier technique of pouring resin into the open bottom-mould and then letting the top part sink down into the resin and cause overflow.
After this, I wiped vaseline on the rubber face, paying particular attention to the keying impressions which must be thoroughly coated with parting agaent but not choked up with it. The vaseline (which I forgot, in a rush, to use in the first pour, hence the leakage) can also be used to block the gaps between the bricks.......
The second pours are setting as I type.