"...I don't know if that is still the case or if they have improved Thompsons..."

Thompsons has a different version out now in addition to the original formula, put it on the deck a few weeks ago, so will have to wait and see if it is better.

Also place Thompsons on any pressure treated lumber (cut ends and all sides before installing) in a horse trailer floor, and it seems to help the wood resist horse urine and manure better.

Sometime in the distant past I read that pressure treating lumber opens up the pores and grain somewhat, and applying a sealer helps.