Does rust get bad enough to cause problems with u-joints? I wouldn't think a relatively large thick section like a u-joint or yoke would be much effected by rust - I'd expect thinner sections like the body sheet metal, frame, etc to be more effected. U-joints are also going to be spinning which will help throw water and junk off and more or less self clean themselves. I'd expect the worst rust problems to be where pockets of mud/salt/muck can build up.
Personally I think I would be more concerned with putting a liberal coating of anti-sieze or similar on the u-joint cups and any bolts to hopefully help keep things from rusting together. But, I'm a left coast sort, so may be a bit out of touch with right coast problems....