I used PVC Electrical boxes and PVC FLEX tubing (LOWES) on my OFF-ROAD POPUP Trailer wiring. The underbelly of my trailer does not have the membrane enclosure and I was dragging some of the original wiring off being OFF-ROAD alot.
I used these items to go through the floor or front wall to get to the batteries.

When going through the wall or floor I drilled a large hole in the bottom of these electrical boxes and then mounted them upsidedown under the floor using sealent to get a good weather seal.
Then I run 3/4-inch PVC flex tubing to interconnect all of the service points that went through the floor to the cabinet areas.

I too used those plastic cable bushings guards on the top side of the floor inside the cabinets. This dresses up the wiring real nice.
All got sealed up just fine to protect against weather and insects etc...
Another plus for me was each of the PVC electrical has removable covers which allows me to route new cables as needed.
My new cable layout shown in Blue looks something like this floorplan drawing of my POPUP trailer...
This is probably an overkill for your project but sure saved the day for me protecting my cables routed under my trailer.
Roy Ken