So, after a couple of Friday afternoons playing with my circular saw and some more reclaimed 15mm ply from work we have the basis of a fiddle yard with traverser

The slides are IKEA drawer runners complete with soft close mechs so the fully shut position is self locking - god bless bargain corner

The wooden uprights from runner to deck are screwed at the front and "mitre bonded" as well as it was impossible to get any other fixing.

here's the underside

I've got more woodwork to do and also it needs dowelling to the adjoining board before I can start laying track etc. Still progress is progress

Oh, the deck is black 'cos it's different ply, thinner but straight, unlike the 15mm stuff I used for the carcass. Didn't fancy trying to brace the deck straight with uprights etc