We have had excellent experience with International Toplac that has lasted well in the tropics (15 years plus). A few mods and
repair patches were painted with Brightside and you are right it failed very quickly.
We started to repaint using Perfection and Primekote but have reverted to Toplac. Our previous experience of Toplac has given us confidence to use it again.
Perfection is not easy to use and the preparation and application of Primekote is much greater. Further we have wasted a huge amount of Perfection because the hardener goes off really really quickly, open the tin and you have to use it virtually immediately store it and it is often off before even opening the tin.
International DO NOT sell the hardener separately. Perfection is more difficult to roll and tip and is much more expensive.
If you really want to use a 2 pack poly then contact a car bodywork specialist. Their paint suppliers sell hardener separately, because they know it goes off.