What Dutch said. There is no "drilling" involved, unless you need a hole to route the cables. But you will have "holes" where screws will go through 5/8" plywood. I have a few dozen of them in the brackets of my solar panels, with #10 screws and Dicor as described. No leaks. You already have a few dozen of them around plumbing vents and square vents with clear cover and God knows what else. Put plenty of Dicor under the mounting foot - it will squeeze out as you tighten the screws - and lubricate the screws with same Dicor before driving them in.
You might need to drill a small pilot hole for when you hit the rafter (and it's a good idea to hit the rafter with at least one screw). Drill very thin 1/16 hole first and run a piece of wire to see if there is a rafter there or not. Normally, you can see the approximate rafters location under the rubber on a wet day and/or near the trailer sides where there are more screws holding the plywood to rafters.
The cable you can route either under the mounting foot - and then you do need a hole, or through the side of the fridge vent "coaming", it's a plastic 1/8" thick. Then you route the cable through the side of the fridge cabinet to wherever you need it.