The snorkal is not really to avoid getting water in the engine. Its to avoid getting dust in the engine. The idea is to lift the intake point up higher so its hard for fine dust to enter the airbox. The only way you could ford deep water is if your electronics and computer were sealed and modern consumer cars are just not designed with that in mind.So the previous two guys posted without any knowledge to answer my question. Anyone else?
The cab vents on the back of the cab, located between the bed and the cab, will let water into the cab if you are in deeper than the wheel wells.So the answer is, not that much water will enter the cab. But what is "not too much water"? That's going to be pretty subjective.
The cab is mostly sealed. There are only two spots on the firewall, high up, with heavy rubber grommets for the wiring looms. The doors are indeed double gasketed. But no-one is going to give you an "ip" rating on these trucks. So your question doesn't have a straight forward answer.
Love smartass replies like yours though. My knowledge is restricted to a couple medium-deep water creek crossings. No water intrusion. But I haven't driven through a lake yet.