I’m so accustomed to the lack of rain here in California that I didn’t bother to check the forecast earlier in the week before taking the van to work. I had only half-completed the roof vent install, leaving the final waterproofing. One torrential downpour later I discovered that the waterproofing was needed!

Nothing major, just a bit of water on the mattress, so I dried that out and made sure to park the van under cover until the weekend.

I decided to use Dicor 551 non-levelling/non-sag lap sealant, rather than the more commonly used Dicor 501 self-levelling lap sealant for waterproofing. The non-sag lap sealant gives a much nicer bead around the edges of the adapter, and on the screw heads.

Before adding the Dicor, I also checked the tension on all the nuts, but the lock washers seem to be doing what they’re supposed to. The butyl tape is still oozing out a bit, which is good.

Compare non-sag:


With self-leveling:


Self-leveling install photo is from FarOutRide who have a bunch of great van build resources on their site.

I did use some self-leveling Dicor on the flat surface of the flange - it does level out nicely:

added self-leveling

There are many more fan install descriptions, using different techniques: