urethane and polyester both react to uv rays. swell and shrink . in the ladder of resins epoxy is at the top . once cured it will not react to uv. there is nothing better for corrosion protection and adhesion than epoxy. but all epoxies are not the same. dplf is useless .
i have done epoxy only since 05 . urethane primer is ok for collision work but as a high build it creates too many problems .