I found out real quick I needed conduit under my OFF-ROAD trailer. It doesn't have the covered membrane like yours but on my first trip to the woods I snagged several of my under trailer rats nest type wiring and had to do some quick twist and tape jobs to finish out my camping trip.
I used 3/4 inch PVC flexible conduit and also installed some upsidedown PVC junction wiring boxes that accepted 3/4-inch conduit.
The electrical junction boxes with a large hole drilled in the bottom of it are mounted where wiring came through my floors usually inside a cabinet floor. I made a round-robin approach and now I can fish wiring all the place and still be inside the PVC CONDUIT. This also solved my uncovered holes and other ways for insects and critters to get into my trailer. Everything all sealed up now from the bottom.
You can get an idea what I did from this floor plan drawing showing my 3/4-inch path in BLUE.
This is the the type of PVC Electrical junction boxes I used. These have weatherproof lids so I can remove those from the bottom and route cables real easy from point A to point B... (ALL FROM LOWES)
Might not work so well if you have covered membrane on the bottom of the trailer.
I use this flexible conduit and electrical junction boxes idea for all my wiring mods... Best way i can think of for going thru a wall or floor.
Just food for thought
Roy Ken
My Posts are IMHO based on my experiences - Words in CAPS does not mean I am shouting
Roy - Carolyn
RETIRED DOAF/DON/DOD/CONTR RADIO TECH (42yrs)
K9PHT (Since 1957) 146.52M
2010 F150, 5.4,3:73 Gears,SCab
2008 Starcraft 14RT EU2000i GEN
2005 Flagstaff 8528RESS