If you are willing to do the prep (ie sand blast, as you've chosen) there is a possible advantage to the epoxy and urethane on a chassis.
For ease of prep and application the POR 15 beats it (use their wash and "metal ready" prep).
Glad to hear you have a plan though, let us know how it turns out.
If taken care of (ie not driven at bonneville and neglected afterwards) both should be fine in 15+ years from now, if properly applied.
