Painting Styrofoam?

I’m building up my Lowe 1440 and putting in an aluminum floor, fastened directly to the ribs, with sheet blue/pink Styrofoam under it. Some have voiced concerns that even though the foam is closed cell it may eventually soak up water. Now I was thinking that I had a few gallons of a latex basement waterproofing paint left over from a project and this might be a place to put it to good use. The possible upside is waterproofing and perhaps fuel “vapor” proofing the foam and the only down side I can see is slight added weight. Any thoughts one-way or the other on the paint? Bob

Bob, IMO, the gas and oil that drops into the boat over time,
then, with water added, it is spread under and around the foam.
This would happen over time, not over a week or two - but months.
If your basement paint could make this barrier, then you are on to something.

and the only people that I know that worry about weight is the "ultralight backpackers".
They go to the extremes of cutting a toothbrush in half, measuring out toothpaste
for how many days they gonna be on the trail. Cut their shoelaces off to the point
they just hold. Precut toilet paper for the amount of days of expected use.
they will drive you NUTS with their fanatics !!

The amount of paint you put on, will only weigh half after it is dried and cured.
Maybe even less than half, if anyone ever wanted to paint a bunch of boards
and tally the results.
Just fix up your boat and go boating !!!!!!!!!!!!!!!!!!
Good Luck

try it in a small area first. some sytrofoam melts when painted.