For the price of the 2 x 4 and considering the involvement and investment of the build, I would find another one and preferably not stored outside. Bring it home and coat it with the cheapest water-based varnish / sealer you can find to stabilize it a bit. If you can find a lumber Co that has lumber laying around inside, you stand a better chance of getting a piece of wood that's stabilized a bit rather than the Depot where fresh studs arrive daily and half of them sit on open trucks.