The pipe being clear is a red herring, it just happened that the supplier had 36mm OD which is the precise size I needed for the through the roof fitting I bought at Lincoln for £5 (£37 on ebay )
Pipe £7.99 delivered
Actually being clear means I can put an LED aircraft warning light in there too
One query - condensation in the tube, only ask as we get some in the tv aerial pole if its left up overnight. and when its fully down none of the pole is 'outside' so no condensation (although the inards of the aerial are shot because of the condensation)
Yes that can be an issue but the acrylic is less likely to be a problem than aluminium. Also as it is transparent I will see it if there is any.
I can always fill it with expanding foam as a cure if required.