I'm writing specifically about our '08 3465SA Montana, but I believe all newer Montanas have the same sort of utility cabinet setup for water and cable TV connections, etc.
The hose pass-through from the utility cabinet had threaded caps on the top and bottom, both of which were extremely difficult to remove. I tried spraying WD-40 and Silicone spray on them, but had to use a hammer whenever I needed to remove the caps to pass the hose through. I finally had enough so here is my solution.
I purchased a residential toilet mount from a hardware store, along with a short outside-threaded 4"ID PVC pipe to thread onto the toilet mount, and a short inside-threaded 4"OD PVC pipe to slide onto the 4"ID pipe and thread a cap to the other end.
I removed the factory caps and flanges, then attached the toilet mount, with the 4"ID PVC pipe attached and sealed to it, to the underside of the Montana, where the original flange had been. I used sheet metal screws to attach it, then applied a liberal amount of silicone sealant around the edges.
Next, I applied sealer to the outside of the 4"OD PVC pipe and slid it in from the top down into the 4"ID pipe attached to the toilet mount, with the inside threads at the top. I again applied a liberal amount of silicone sealant around this pipe and the floor of the utility cabinet.
With everything sealed at the top and bottom holes, and the pipe running between the two, there is no outside exposure to the area between the utility cabinet floor and the underside of the Montana. The thread on cap seals the utility cabinet when the pass-through is not in use, and this design cap is a lot easier to attach and detach.
I am happy with this new setup. It was definitely worth the effort! I hope this information us equally useful to others.