So if you made your box 3' wide by 7' long by 4' tall it should hold two guys. That will displace 84 cubic feet of water, which at 62 lbs/cubic foot will need over 5,000 lbs of ballast. What kind of jon boat did you say you have? Like most hunting results are not assured. I've hunted the curtain blinds several times because I like the experience. But the only time I've killed more than one duck in a day was when I doubled on pintails about 10 minutes before sunset and that was the only shot I got that day. I've just never been lucky to hit the wind and weather needed to make it work. Maybe this year!