I build the boxes for doing the moulds of the Hunt Typ II Destroyer for cruel Seas.
I cut the base out of extruded polystyrene and glue the pieces to be moulded on them with hot glue. then I build a box out of lego around it. The bottom and the walls are fixed with brown tape ( the one you use for packing parcels for the post). Then I spray the inside with mould release agent. Before casting I place the boxes on greased paper for protection of my worksurface.
I pures in the silicone last night . So will have to do the second side of this mould:
The others are single piece moulds.
Will cast the first ship today if all goes to plan.