Duplicolor is a good brand to use for what you need. As for the flexing, you can get a rattle can of it at the parts store. Just follow the directions and your fine. That's what was recommended to me by my auto body teacher.
You can't lose if you put God first!
1989 LX, 306 with TF top end kit, Anderson N-21 cam, TKO 600 trans with steel splatter shield,full Maximum Motorsports Mustang maximum Grip box, Detroit locker rear end with 31 spline Moser axles. Staggered wheels with Nitto 555 315/35/17 out back.