This post explains how I replaced the 6" circular pop-up vent in the bathroom ceiling of my U-Haul VT-16 with a power fan unit from the same manufacturer. Having a fan in the bath will more effectively exhaust any moisture or odor.
The Ventline Van-Air Powered Roof Vent came from Tweety's RV. It was about $50. Unfortunately, although the photo shows a Colonial White fan, the part number, and the part delivered were the "polar white" color. I was pretty much expecting this based on the part number (VP-543 PW), and the garnish is small enough on the interior that in practice it isn't a big deal. The item # 31-8008, and it's a power fan, not a power vent!
Both the original vent and the fan were manufactured by Ventline and have very similar construction: The size of the motorized fan housing is identical to the original vent. The vent part of the mechanism even works the same. Pushing up on the handle drives up couple tabs that support a bowl shaped vent cover on the roof, creating a small airspace. However the power vent incorporates a switch and fan in the mechanism, and the screw spacing and securing method are a little different:
The non-powered vent mounts in the ceiling of the VT bath using three long screws that pass through the interior garnish, then through the both inner and outer hulls and into a heavy aluminum casting on the exterior that carries some tinnerman nuts. Tightening the screws clamps the inner garnish and outer plate tightly together. A plywood spacer installed between the hulls between keeps them separate and rigid. Then a semi-translucent windscreen screws on top.
The fan-powered vent is a little different: None of the screws pierce all the way. It has a similar inner garnish that carries 3 screws on a slightly different spacing. Those pierce only the inner hole and anchor in the plywood. The outside frame is screwed with multiple screws to the outer hull/plywood sandwich. The outer housing is a light painted steel component and not a heavy cast part.
A word about access. Having a ladder the right height made this installation much easier. I noticed as I was working that there were a bunch of spider cracks near this spot, probably caused by the installer of the Swamp Cooler or somone doing some work putting a lot of weight on the roof of the trailer in an unsupported edge.
Removing the old vent:
The hardest part of the project was removing the rigid outer frame of the old vent. It was VERY securely cemented to the outside of the trailer with copious silicone adhesive. I could barely slip a utility knife blade between the outer hull and the frame, and could only get it in about a 1/4 inch at a time. Working my way around the exterior bit by bit, I was finally able to get a toe hold by cutting in to the depth of full depth of the adhesive and worked my way around to the back, where there wasn't much room to manipulate the knife. It took about half an hour to pull this off, and I went through a couple of blades.
Damage to the fiberglass surface was very minimal, but there was a lot of leftover silicone to remove. I scraped with a plastic putty knife, my fingernails and finally cleaned up the surface some with acetone. Most everything was going to be covered by the new hardware, so that made the finish less critical.
Test fitting the parts
I placed the outer frame on the roof and oriented it so that the Drip hole was located on the downhill side of the trailer. I slipped the interior section, containing the motor housing in place to ensure that the outside was properly registered. Then I went back up and marked the holes for the new screws.
Before marking the location of the exterior holes, I noticed that the plywood spacer between the hulls was actually made up of a few boards. I am guessing that to match the sloping contour of the trailer roof, they slipped in three narrow boards side by side, measuring about 3/4 thick x 4 inches wide and 10 inches long, then they cut the 6" access hole. A single wide board wouldn't follow the roofline very well.
However, the big hole through the center leaves those side boards disconnected, and a little wobbly and they tend to slip around, so after I marked the locations of the new mounting screws, I put screws in the existing screw holes, and each new hole I drilled to keep things in registration as I went.
Drilling the new mounting holes
I measured and purchased stainless hardware for the interior and exterior screws, and wrapped a piece of tape around my drill bit to serve as a depth gauge and ensure I didn't drill too far from the outside. --ALL stainless steel hardware - don't fool around with this when you have a choice. The trailer is already 25 years old and having removed and drilled out enough corroded screws, I can tell that this is not the place to save a buck! The bath area is definitely going to get wet, and there's even condensation on the interior of the trailer, so get good hardware.
Moving on, I drilled the exterior holes through and into the plywood. I also went back and drilled the hole in the fiberglass just a bit larger so it wouldn’t crack as the screws were introduced.
Extending the fan leads
I found that the leads I had for my fan were short enough that it would create some problems accessing them, so I opened the fan housing and attached some longer leads. It could have been done externally but I don't like to leave connections or wire nuts where I can't get at them. In this case I soldered red and black wires to the existing switch and motor connections and ran them out along the original wire locations. I routed the new wires through a hole I drilled sideways through the plywood toward the closet access. If I didn't have this handy angle drill I probably would have had to slip out one of the boards and trim one or somehow or create a gap between boards.
I made a gasket from Butyl Tape I bought at camping world. This was the first time I used the tape. I applied it to the housing edge carefully and ensured that it covered all the screw holes. I probably could have used more tape than I did - it cuts off pretty easily afterwards.
I filled the existing three screw holes with some of the butyl tape. Now I aligned and set the outer housing. Repositioning the outer housing carefully I had to poke a couple screws through the screw holes in the tape so I could align things. The tape grabs pretty quickly and resists fine readjustments. I put the inner motor housing back in place to keep things registered, aligning it so that it did not quite overlap the existing screw holes, which were close but not quite on.
Test the fan
I tested the fan one more time by connecting some 12V test leads before screwing down the housing onto the tape. Working my way around to each screw several times, I tightened the bolts crosswise and the tape pressed out slowly.
Mount the inner garnish
Finally, I marked the interior holes and drilled them out using my drill bit / depth gauge and went back and drilled the fiberglass hole just a bit larger. The gel coat can crack if the screw is an exact fit, so I rely on anchoring in the plywood, not the fiberglass.
Finishing up, I screwed everything together securely, connected the 12V and confirmed everything still works! The result was a nearly stock appearance with the added functionality of a powered fan. Experimenting, I discovered that the roof solar generates enough power in full daylight to run the new fan at a decent speed, so I may add a switch somewhere to let me choose between trickle charging and operating the fan.