I've had good luck using low tack blue tape to mark off a square cut on the tube, then cutting with a jigsaw using the finest blade I was able to find. I use a variable speed jigsaw and keep the speed setting fairly slow and apply minimal pressure. Once the cut is done I use a palm router with a 1/8" roundover bit to clean the burr off the cut. It should look like a factory edge if you take your time.