Frank - every old bed I've seen is the most rotten along the edges where the strips sit - a problem because of differential reaction to temperature cycles, and the fact that moisture collects on the metal first when it gets cold
my bed boards were individualy painted all 6 sides w/ marine enamel and fit together, bolted to the cross sills and then the whole assembly got another good coat top and bottom to seal the joints - haven't had any problems w/ swelling or shifting in a very wet climate [daily driver], so I think I got'em pretty well sealed
the wood is actually out of a 100 year old house I helped tear down and is from first growth trees - the kinda straight close grain wood ya can't buy any more!
Bill