pipe through the floor

I am in the process of redoing the gas pipe and adding some wiring. One of the weakness of how Compass Rose was built is the lack of attention to keeping water out of the underside of the trailer and potential of leaks from water spray when traveling, not to mention some of the holes are big enough to allow critters to climb in! I have been looking at bulkhead fittings which essentially are an additional pair of connections (which I do not want), one above and one below and all I want is some way to seal things up and keep wires and pipe from rubbing/shifting. To complicate things a polyethylene membrane was used to protect the underside of the trailer so this needs to be part of the thinking.