I decided to replace the existing vent caps along with the new vent pipes. I ordered three from Vintage Trailer Supply.
First I had to remove the old ones that were caked with silicone sealant.
I removed the old vent pipe and carefully scraped off as much of the silicone sealant as I could then lightly wire brushed the area. I placed a short piece of pipe in the opening to help locate the new cap.
I trimmed the cap so it wouldn’t overlap the trailer seam, drilled a hole in each corner and ran a bead of parbond sealant around the underside and riveted it on. I put tape 1/8 inch away from the edge of the cap and spread sealant around the edge.
The tape helps control the sealant and leaves a clean look.