Great test
Is the best way to quantify water absorbtion visual or by weight?
I have been thinking about trying this but don't have all the different sealers.
Use a very accurate scale. Might have to borrow one from a science teacher or your neighborhood drug dealer
Each block would start off at the same weight.
One block would have no treatment as a control
Each block would be sealed with a different method
Each block should have a thru hole and a perpendicular hole so they are similar to actual conditions
After sealing prime and paint?
Immerse in water for some amount of time to simulate actual conditions and then let air dry till free water is gone.
Weigh and compare.
I believe different woods have vastly different rates of absorbtion and this makes a large difference in how the wood acts upon exposure to water.