I have made so many different PVC rails over the years and I am in Minnesota/ North Dakota so it gets and stays extremely cold here most winters. I had two shot gun rails that were made out of 1 1/4 in pvc, that is the smallest I have used and it worked but in one season I had to replace two of the four pipes. I have one that is made of 3in pipe and that has lasted a number of years!! I also recently found some 5in PVC that was only like $6 for 10 feet (on sale) and it is nice to work with because I just build three independent legs and screw them into the pipe, and it is sturdy enough to hold. Saves a lot of time!
Sorry about the long ass post! Pm me if you have any questions!