Reference your comment: For low power applications you can use small
plastic blocks, available at DIY stores. These are normally used for
building cupboards and have a
hole at each end and one at right angles in the middle. Size about 30mm
long and 8 mm wide.
I have also used these for many years, usualy singularly but sometimes in
series for very high voltages (> 10Kv). The are quite good and less
affected by the weather and uv than plastic pipe but I still prefer the old
73, Roger, G2AJV.