I will tell you right now that sealing the foundation is a waste of time. Unless your house is a house boat, it won't float, so you might as well stop thinking about all the ways to keep it from doing that.What you should do is check for the two usual culprits of crawl space flooding: clogged gutters and improperly sloped soil around the foundation. Your gutters should be clean and free of debris, with at least one downspout for every 600 to 800 square feet of roof surface. Make sure the ends of the downspouts are extended to discharge at least four to six feet from the foundation. Spouts that discharge too close to the foundation are like big fire hoses blasting water into the crawl space.As for the soil around your foundation, you want it to slope away from the house to keep rainfall from collecting against the foundation walls. The angle and type of soil are both important. The soil should slope downward six inches over the first four feet from the foundation wall. After that, it can be graded more gradually but should never allow water to run back toward the house. If your grading needs improvement, use clean fill dirt (not topsoil) to build up the soil around your house. Tamp the soil down to the correct slope and finish with a layer of topsoil and grass seed to prevent erosion. Stone or mulch works too.