Very unusual for that tank to leak after a new OEM O ring is used. All of the suggestions here are good and really don't add much time the the replacement. Cleaning top and bottom shell, lightly lube the top and bottom shell or put a glob of lube in the palm of your hand and pull the ring through it. That gets a light coating all the way around the ring protecting it completely. Light means the ring is shiny with the grease, that's all that is needed. Tapping the clamps as they are tightened in a star (crisscross) pattern should help. If it still leaks you will have to check for a crack, or carefully examine where the leak is actually coming from. See if the air-relief assembly has a slight leak. It will flow down the tank and look like the tank is leaking at the O ring.Nope, didn't lube it.
Those tanks have never been known to warp, regardless of the climate. They are actually the strongest filter tanks made in this country. I installed the second one in my area (got it as a "try me" from the local rep, lower cost) right at 30 years ago and it is still going strong.