I picked up this idea from Charlie Kuss who's building an 8A in the USA.
I still used the Vans Capacitance Sender Kit but replaced the nylon washers and PVC tubing by making some Delrin (Acetal in the UK) spacers and washers from a 1" rod on a metalwork lathe.
The hole size I drilled in the rib to accept the spacer was the 4th step on the Avery 3/4" Step Drill (about 0.55"). Otherwise it's pretty much as per the drawing that Charlie sent me published at my website:
