I want to emphasize what someone else said - by all means sign and date all drawings, etc. but have them notarized as you go along. A date can be faked on anything.
And be prepared to litigate over any infringements on your patents. if you have a successful product, the sharks (not the ones in the tank) will be out to steal, "modify". whatever. If you ar enot prepared to defend in court, your patants are worht nothing.