schedule 40 will be fine, "schedule" 40,80 or 160 are the pipes spec data referring to its pressure ratings, as a liquid carrying vessel. its a bumper or whatever dont worry about the schedule #'s.
#8 on your list should be : duct tape one end of the pipe, fill with water ( FULL!) and tape the other end then bend. this will act as the pipe being solid and help reduce flattening.
Water is not a solid and will leak through even the best duct tape job especially under pressure. I you want to try to support the inside of the pipe, use tightly packed sand and try welding caps on the ends.
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