I built the SR in a hurry, so didn’t add a ballast tube.
I did put one in the Big Gulp, and when full, puts total weight at 4 1/2 pounds. Then I added another 1/2 pound externally, and it still worked great in a 25 MPH breeze. If I figured correct, that still only puts loading at 19 oz/sq.ft. Next time, I’ll add lead till I can’t launch it!