Thanks Martin.I wasn't after an exact measurement as such,but what you say makes sense.I have managed by some fluke(certainly more by luck than judgement,or even some dodgy measuring) to have no electrical connection at the wing rails,so only have to put gaps in the crossing V rails.
That only leaves me with the electrical bits and a frog switch and all will be done.
Oh,and while I think about it ,thanks for Templot,it's been a great help.
ATB
Phil.