I have the same L&M Mako Housing for my PC-350. I put it in the bathtub for a few hours without the camera. I also put a folded up paper towel in there to see if there was any moisture on the paper towel.
Doing this is not being "overly cautious." It's being smart!
I would rather know if my housing is going to leak in the bathtub before I put my camera inside the housing and take it into open water.
After the bathtub test, I took it into a 13' deep pool.
You should also think about buying a Drying Agent "Moisture Muncher." You should be able to get them at a dive shop that sells housings. They are little packages of crystals that are in their own little package. They fit nicely in the housing right next to your camera.
I'm going to copy what the instructions say.....
<Moisture Muncher will only be effective when used inside an airtight container (i.e., <waterproof case, thick, reseal able plastic bags, etc.) along with valuables you want to <keep dry. The area inside the container will become moisture free. Every time the <container is opened, the moisture level will rise again. When you close the container, <Moisture Muncher can once again remove the moisture in the container. The more times <you open the airtight container, the faster the indicating crystals will turn pink. (the <crystals start out blue).
You can also reuse these twice. Once the crystals turn pink, you can bake the packs in an oven no more than 93 degrees for a couple of hours. The crystals turn blue again.
Have fun with your new housing. I love mine!