I am the only one I know of on this forum that is using what I call large deep tubes. They are simply made out of sheet plastic obtained from Home Depot. They are made from 4' by 8' sheets. They are rolled into a round tube with a four inch overlap which is glued. The rough approximation of the circumference of a circle is pi * the diameter Therefore the approximate diameter of the tube will be 44/3.14 = 14 inches.
However this is much wider than needed and taller is better. The deeper the tubes the less roots that will be laying in the bottom of the tubes. So picture pushing in the sides of the tubes until the tubes are only six inches wide and are essentially now a rectangle 12.6 inches tall and six inches wide with a 6 inch diameter half circle for a top and bottom. This makes each tube 6 inches wide and 18.6 inches tall.
Home Depot sells FRP panels which are stiff and need to be heated with a heat source to bend down to a 6 inch diameter circle. They also have really flexible cheaper panels that are flexible enough to easily roll. The sides of these tubes need to be glued to each other and the trough sides though. The tubes are simply forced into a plywood trough with an inside measurement equal to 6 X the number of parallel tubes used and the inside height of the trough is 18.6 inches.
Narrow strips of wood are attached to the top of the trough every few feet to keep the trough from bowing and to keep the tubes from popping out if using the stiffer FRP sheets. A hole saw is used to make the holes for the net pots. The ends are simply cut in the shape of the rectangle with the tow half circles. Cover these on the inside with the plastic and simply force fit them into place. Cut an inch off the bottom of the ends plates at the drain ends and simply drain to plastic gutters.
The cheap flexible sheets are simply polethylene plastic like a rubbermaid plastic. They are simply opaque white sheets. There are no really good solvent cements for polethylene plastics but Weld-On #1829 works pretty well. The preferred method of handling the seams is to preferred them. I use a plastic welder by Laramy but there are some simple cheap ones sold on ebay that work really well with this thin plastic. These only cost about 50$
http://shop.ebay.com/?_from=R40&_trksid=p3984.m38.l1313&_nkw=plastic+welder&_sacat=See-All-Categories versus a used Laramy at $250 or more.
http://cgi.ebay.com/LARAMY-PLASTIC-WELDER_W0QQitemZ370324052616QQcmdZViewItemQQptZLH_DefaultDomain_0?hash=item5639089a88 The Laramy requires that you also have an air compressor. They work exceptionally well though.