Oh boy....
I do agree that bike tubes are porous. No argument there. And after trying numerous brands and qualities, My experience would indicate without sealant, they ALL leak.
When I'm installing sealant, I put it INSIDE the tube? If installed in sufficient quantity, the inside would be coated as the tire rolls, right? As the bike hits bumps the sealant is splashed, eventually coating the entire inside of the tube.
After going with the sealant, my tires that needed to be check weekly, went to the need every couple of months. They DO still need to be checked on occasion.