And I do have personal knowledge of that. I received 5 rather large screws that look just like lag screws in the x-rays, in my left ankle about 20 some years ago in an automobile accident from a drunk driver and it still hurts like hell to this day! Thank you. You can purchase good straps, that I would doubt, will deteriorate any time soon. And I'd have to agree, the lag screws would last longer. I have some straps at work, that are left out in the elements all the time, and I work them as if they were new. They are nice, affordable, ratchet staps, used to secure heavy loads. (not the bargain basement ones). Given the diameter of the trunk. and where you will be securing the antenna, they should work just fine and they will last a long time if you put the antenna on a piece of pipe for a mast. If they are good one's, tighten the snot out of them. It may not be plumb, but it sure will work. They are constructed to endure uv's. You could still use lag screws, but I was just giving you an alternative to hurting the tree. You could put a lag screw in you hand, and the wound would heal, in time. Bet it would hurt like hell though.