Vira has six small opening ports. Replacing them took one summer: a routing template, a CNC-cut angled shim for every port, new plywood panels inside, and one mistake along the way.
Ports: a template and a mistake
In February 2022 I made a jig to cut the port openings. The ports I bought have an angled spigot. That's good for drainage, but it's a lot more work, because the cut through the plywood core has to follow the angle. My router bit is only 2.5 inches long, so the template is made of two layers: it lines up the cut in the outer skin and sets the angle.
In July I took the first old window out, to see how it's done. Pull the trim, cut the side of the frame, fold it inward and pull it out. Then the template, and route the hole. The old opening was 3–5 mm bigger than the new port, so there wasn't much grinding, mostly the slope for the spigots. I added a sloped plate inside for 2 more degrees, and measured the thickness for the screws: #10, 1-1/4 inch.
Then the first port went in, the pilot. Short story: I bought self-draining ports by mistake, instead of rain-draining ones. Not a big difference, except that the Irwin 34 cabin sides are 17° from vertical, and self-draining ports allow 15° at most. So I needed the inside wall closer to vertical. I calculated that 3 degrees more would do it, and put a sloped shim inside, under the plywood. I also added some reflective insulation to cut the heat coming through the cabin sides. The port went in on 3M 5200, as Bomar recommends.
I had planned to through-bolt the ports, and even bought the bolts. Then I changed my mind and used self-tappers, like the original. With the tilted spigot, the bottom bolts came too close to the edge, and the top ones came out under the outer frame. And a 1-inch #10 screw will break the plastic before it pulls out of epoxied plywood anyway. If a storm is strong enough to break the windows, I'll put covers on the outside instead of trusting screws.
Five more ports
With my son's help I took out the old, cracked, leaking plastic windows. Metal ones will come later, or much later. We cut the old ones out, removed the old inner plywood, and added the slope shims, CNC-cut so the angle is exact. Another 1/2-inch plywood strip below each window supports the interior plywood. The old sealant, which looked like 5200, hadn't held to the plastic. I'll ask Bomar what prep they want.
Then I cut the inner plywood panels and epoxied them in, held with wood screws and temporary plates on the outside, ready for the other five ports.
In August came a long day: route five new openings with the CNC template. At the thickest spot I had to cut through about 1/4 inch of outer glass, 3/4 inch of original plywood, about 1/2 inch of angled spacer and 1/4 inch of inner plywood, and none of it was square. Even the 2-inch bit couldn't reach. So I routed with both templates as deep as I could, took the add-on template off, and cut deeper from the top.
Lots of dust. The ports went in on 5200. Maybe not the best choice, but the maker strictly recommends it. I soaked the openings with sealant first, then pushed the port in, so there's solid polyurethane between the port and every layer of plywood and glass.
It doesn't take many words to tell, but it was a hell of a lot of work: cut, clean, mask, seal, and figure out how to clamp the outer trim rings on a curved surface. Sand bags help, as usual.