Regardless of whether the key fob is inside the car . . . to unlock the car you need a key fob *outside* the car (or use the key) - i.e. unlocking a previously locked car by touching the door handle with the key fob inside the car and none outside will *not* unlock the car.
I removed the key from my key fob, left the key fob inside the car, locked the car using the key (not the key fob), then tried to unlock the car by touching the door handle - I could *not* unlock the car. I then unlocked the car by inserting the key into the keyhole on the driver door.
Remember unlocking the car is one thing - to start the engine you will need the key fob.
OP's intent is doable - remove the key from the key fob, leave the key fob inside the car (hidden of course) and place the key in the wet suit.