Just got back from the lumber store,and could not find one single straight 2x8.They all had a slight twist just like the ones I used on my stand.If I used some weight on the frame to straighten it out then applied my plywood,would that keep it straight.
I couldn't find any straight 2X8's when I built my stand either. So I bought 2X10's and ran them through a table saw and they were a straight as an arrow with 2 square flat sides.