I bought a new poplar board instead of trying to fix the warp. Yesterday afternoon I milled up the sides. This morning I milled up the rails. I have the rails milled and tenoned. I ganged the rails and cut the tenons on the table saw. I also have one side mortised and roughed out on the bandsaw.
I'll have to take a trip out to the base to use the spindle and belt sanders to clean it up. Once I get the side sanded and finished out I can trace it to the other side and cut that one out. I did make a mistake when cutting the tenons. I made a mis-cut when cutting the tenon on the table saw. Just the width of the saw kerf, on one side of one tenon. So I glued a little repair on there and will whittle it down somehow.