[Justfishin']

Mahogany is a good hardwood to use in that it works nicely and resists water damage. The downside is it's specific gravity is a little heavy and it won't take take much weight to go sub-surface. I find it best for poppers, pencils and deep swimmers. Suckers cast a mile.
I agree w/ the Prof. about searching here, and with Slipknot; cedar is better for floatability and being able to adjust action through weighting, just not really durable with toothy critters or rocks. Still, it's what I make most of my plugs out of.
I seal all my plugs before paint & rigging with 50/50 spar varnish/Waterlox- which is a modified tung oil- which I then thin 50% with naptha for penetration. I put them in a sealed container until I remember to take them out- at least overnight, and then let them dry for a couple of days. With a quick scuff from a Scotchbite pad,the paints I've been using (mostly spray cans, some automotive enamels) hold very well.
Try the library for Bruce Hoadly's "Understanding Wood" for a book on the properties of wood and wood products.