Stainless wire from each leg to the PVC with some turn buckles will sturdy her up nicely. I have roughly the same set-up on an 85 gallon barrel and the wire/turnbuckle combo works great with my long 53" PVC tube.
Will the pipe really not hold up? I never considered that.
It'll be fine sir. Like I said mine is 53" in length with only 4 self tapers holding it to the drum. Adjust the turnbuckles and make sure the wire/rope/straps are slightly upward and you'd be surprised how rigid it'll be.