It is open to debate whether resin casting carriages ends up saving you much time and effort over scratch building the parts in styrene.
Yes, it is undoubtedly much quicker to cast a number of them once you have made the master and the mould, but it takes rather more time to clean them up and get them ready for gluing together.
For example it was an evening's work this week to tidy up the bits for Superbarn 117.
It's also the case that when you come to build up the carriage that comparatively brittle resin is not as easy to bond and work with as soft, melt-able styrene.
Very much in its favour, however, is the fact that the whole body side is much more rigid and robust than one fabricated out of styrene.
Next time you seem them here I hope these eight pieces will be a single carriage body.