I also used some 10-12" corrugated drain pipe. One piece was long enough to make a long tube for the main/boom and a shorter tube for the jib and hotstick. This corrugated pipe is also double lined with a smooth inner surface so the sails slide in easily. Despite it being black, the inside actually stays pretty cool because of the double wall construction. The corrugated shape makes it pretty easy to secure them as well - I just used some threaded rod and angle iron. The ridges help secure it from forward/backward movement. I cut plywood circles to fit inside the ends and secured them with drywall screws and caulk to seal it, then painted it black. I did something similar for the rear access hatches, minus that whole sealing it shut part. Used some fence latch mechanisms and hinges from Home Depot to allow for pad locks. Also left a few inches of the piping to hang over the doors for a little rain protection (not sure if it does any good). Haven't had any issues with moisture. All in all I think I spent < $100.
