Think I'd be more worried about wet pants than wet plugs!
Like Mini13 says, crank sensors shouldn't be an issue. They are sealed units, and wherever you put them they'll likely have an external wiring connection. Do make sure they can't be knocked out of position though. You could rig two ignition systems with crank sensor(s), omitting the need for a cam sensor and giving you wasted spark with fail safe redundancy - OTT I know.
Having seen your engineering skills, I'm sure you could knock up a clamp, or something, to improve the boot to plug seal.