Eric - Propane is dangerous stuff if you don't handle it correctly. I have attached an old copy of the ABYC code. There is a 2006 revision which I don't have.
It looks like you just bored a clearance hole for the LPG line coming from the regulator. This is a major NO-NO because it allows gas to escape into the lazarette, engine compartment, and cabin. Any leakage must be allowed to exit under the tank and out of the boat. The seals I used are available at most chandleries, Defender, WM, etc.
BTW, the vent has to be checked periodically to be sure there are no spiders in residence or other blockages. I use a water hose to clean it out.
You should have a gauge mounted on the input to your regulator so you can test for leaks. Using a cigarette lighter to check for propane leaks is not good practice. The gauge is required to meet code.
Similarly, you should have a solenoid valve after the regulator so you can easily turn off the tank after use. You do not want to discover an open stove burner with a loud bang. The solenoid valve eliminates the need for a main valve inside the boat per code. I would mount a new breaker for your macerator since the wiring exists for the solenoid and the panel is labeled.
The tank should be restrained so it can't damage the regulator in a seaway.
Making these changes will greatly increase the safety factor when using LPG on your boat and will also get you past a survey if you are ever required to have one.