if you go single barrel, either get an industrial pvc (one of the big blue/green pipes that you see in big piles at construction yards), or use a grey pvc pipe (used for electrical purposes). usually the industrial one is put directly on the snow, or ontop of a small mountain of snow.
the diameter of your pipe doesnt really matter, its just personal preference. but the thickness does matter. if you plan on using the grey pvc, i would suggest getting anything between a 2 inch diameter pipe and a 4 inch diameter pipe (dunno if they make 4 inch diameter electrical pvc pipes) just because the pipe will be big enough to put on a 2x4 on the 4 inch side. so it would look like this:
__
__( )__
|_______|
i think any pipe over 2 inches should make sure that your skis dont hit the 2x4.
and when you go to attach it to your 2x4, drill through the top of the pvc (see the stickied threads in the forum if you need help with that).
if you wanna overdo yourself, you could find small pieces of wood that you could put like so:
__
_..( ).._
|_______| where the .. are the small pieces of wood nailed to the 2x4
this will make sure the pipe wont loosen on the 2x4, and increase the longevity of your rail
lemme know if that helped or if i didnt answer the question at all
