I am the spoiler about propane. (My back up to the induction burner is the small 1# common bottles, which I keep inside PVC pipe on the side of the splash well. I have had well designed systems on my larger cruising boat for cooking only)
Even with the ;propane heater in the cockpit there are risks. The propane is heavier than air, and a leak can accumulate in the cockpit. The same standards apply for in the cockpit as the cabin. A solenoid or manual shut off at the tank, with a "sniffer" in the lowest part of the bilge (cockpit floor). Also storage of the propane tanks where any fumes/gas drains overboard. (A totally sealed Lazarette with drains overboard to the side will meet this requirement).
My personal issue with propane for a heater, is the in-connivance of getting tanks filled. Diesel seems like a better option--less risk, and easier to obtain.
Are these "marine" units designed for outside installation? The installation in an RV is entirely different than in the cockpit of a boat. Yes, I have LP for cooking (use the induction any way), refrigeration and heating in the RV--but the 30 gallon tank is under the unit, all except the stove are vented to the outside--and I have 2 shut off valves--one at the tank, and one (with a sniffer) as the propane enters from below the floor. I also have electric options, and use those 90 % of the time.