With a wooden deck you want to seal ALL sides, top, bottom, AND edges with a good non-waterbased sealer. If you use a water-based acrylic sealer your deck WILL warp (been there, done that). If you don't seal it will eventually warp due to humidity in the air. Thin wood is very susceptible to warping. A hardware store product may be a better choice than one with a model manufacturer's logo.
Once sealed and installed I think I'd go with an ink in alcohol wash.