If you were on sport tek's cationic (sp?) garments, I would say yea, thin out your ink a touch and print white through higher mesh counts....
I do not trust those Gildans to not bleed....
As it is for light garments:
Just like ScreenPrinter123 said... Add ink reducer of choice and print through higher mesh counts, ideally wet on wet to make the ink layer wrap around the shirt fibers for extra softness.