Can I seal the pressure treated lumber so the chemicals dont seep out through the vinyl coated aluminum again?
I answered this question from a different perspective, not knowing the pressure treated lumber may be the culpritThe newer treated lumber often has a lot of copper in it, and can react badly to aluminumYou won't need to seal the lumber, that may not work long termTry wrapping the wood posts in some house wrap like Tyvek or even 15 roofing paper before installing the aluminum trimThis will make a permanent and water resistant barrier between the treated lumber and the aluminumGood luck.
