This has been my modus operandi for the past many years: Take your film and put it in clear zip-lok bags. Ask (politely) that the film be hand-inspected and sniffed by Rin-Tin-Tin, but not X-ray'd. They will tell you that the X-rays don't damage film. Tell them (politely) that you understand that it will not ruin film, but that it does degrade the film's contrast and image sharpness, and that as these are qualities that are important to the technical and legal record useage of the boat pictures you are about to take, could you again (politely) insist on hand inspection. They will closely inspect each roll of film, but I have never been turned down yet. But then again, 1.) I am a professional boat guy so the argument makes sense for me, and 2.) I have not gone thru a US airport since the new Homeland Security (I'm sorry, but that sounds way too creepy for me - shades of "Show me zee papurrs, Komerade!" from bad spy movies) agents have been placed.
Hope for the best, but plan for the worst.