Hmmm your best bet would be to contact various wastegate manufactures as they'll be able to tell you whether or not their products are water tight. Also ask them about their blow off valves (BOV) as well. That would depend though on the style of BOV you were going for, atmosphere discharge or recirculated.

As for the intake (compressor side) on the turbo you would have to install a snorkel typically found on off road rigs similar to the one below although it would have to be custom but you should get the idea.