Issue 21

As mentioned before, this is a very quick one. We're just basically adding padding to the corridor. I've taken the archways out to make installing & weathering easier.

There's 8 pieces, and they glue in pretty much exactly how they look. Do note that unlike the other corridor, this set of top row pads is flush with the corridor piece, thus:

That's about it, really. More skeleton and shell parts, but we'll deal with them at the appropriate time.