Getting a Good Seal when Installing a Fresair S6
and the MaxxAir MaxxFan 7000K
Stephen M Golden
Copyright © 21 February 2023
My first RAM Promaster roof project was to install the Fresair S6 12v cooling unit.
I read the instructions thoroughly and watched many videos
in preparation for installing this unit.
I think I might have taken the instructions too restrictively and erred
on the side of caution when tightening it down to the roof. The instructions said
“Be careful not to over tighten the bolts as this can warp or crack the
base.” (See the footnote on page 3)
This documentation begins with the unit hole already cut and the bolt holes
Fresair provides a “large foam seal” (1” x 3/4” thick) and a
“small foam seal” (1” x 3/8” thick). I
used the large foam around the inner area as instructed.
The smaller foam provided in the installation kit didn’t
seem appropriate as the surface of the Fresair base is a lattice and not
smooth. In addition, the Promaster has
mesas and valleys that are 3/8” high.
The foam did not compress well into the valleys to make a seal.
On watching the videos installing on a Promaster roof, no
one addressed this issue. They didn’t
spend a lot of time describing how they made the seal but just recommended
caulk, lap sealant, caulk and lap sealant, or butyl tape. I saw no indication any of these methods
failed to work for them, but it might not have been something they wanted to
I tried all those methods:
Caulk: fail. Lap sealant:
fail. Butyl tape: fail.
I took me four attempts before I analyzed the situation from
above and below to arrive at a solution that worked.
First of all, the large foam can be applied as the
instructions say. It works except for
the valleys of the roof.
BE EXTRA CERTAIN the hoses are not under the large foam
seal. In my case, while the hoses
weren’t “crimped,” they were under the foam, and I didn’t even realize it. This was one source of leaking for me. I finally noticed that the hoses went up
before they came down into the van.
If it weren’t for the mesas and valleys on a Promaster roof,
I think the large foam is all you would need to get a good seal. That being said, I’m not going to go into a
lot of detail into the methods that did not work for me.
Here’s what I did.
I mounted the unit at the front of the bay area, where there
is a rectangular surface that appears to be designed for mounting of such a
unit. However, it doesn’t accommodate
the Fresair S6 appropriately.
There is a surface that is smooth in the front this
rectangular area. I used the smaller
foam provided to place a strip underneath the front across the entire
unit. Then, I got some High Density Neoprene Closed Cell Foam Tape, 1/2 Inch Wide X 3/8 Inch Thick as
well as some High Density Neoprene Closed Cell Foam Tape, 1/2 Inch Wide X 1/8 Inch Thick. 
I cut wedges to fit each of the five roof valleys at the
rear of the unit.
I placed the wedges into the five valleys under the rear of
the unit. I took a strip of the 1/8”
thick foam tape and ran it across the mesas and on top of the wedges from the
left side to the right of the unit’s footprint.
I ran a strip of the 1/8” foam tape from front to back on each side
because the left and right sides were aligned with mesas, completing a
rectangular foam perimeter.
I applied a bead of Sikaflex 221 sealant/adhesive on the outside and inside of each
surface of the foam where it contacted the roof. I made sure the joints where the foam strips
touched each other were well sealed with the Sikaflex also. I allowed this to cure for a couple of
hours. Sikaflex says it becomes “tackless” in one hour.
I set the Fresair unit into place, inserted the filter unit,
put the bolts in their sockets and through the roof, and tightened them to the
point where I could just see the base of the unit compressing slightly at the
bolt sockets. This worked.
After multiple rainstorms, snow and ice, there is no more leakage.
I had cut the hole for the Fresair with a jigsaw. I cut the hole for the MaxxFan with an angle
grinder loaded with a metal-steel cut-off wheel.
The angle grinder was much easier, and I got a cleaner cut. I recommend it.
Having learned some things from the Fresair installation,
once again, I cut wedges. I needed six
for the MaxxFan installation: three in the front and three in the back. Like the Fresair, the sides of the MaxxFan
were on the mesas. I placed the 1/8”
foam across the mesas and wedges on the front and back and completed the square
by placing 1/8” foam on the left and right.
Then, I applied a bead of Sikaflex 221 sealant/adhesive on each side of the foam square.
Because the MaxxFan requires a minimum ceiling/roof
thickness of 1-1/8” for the “Garnish Trim Ring,” I made a 2x3 square with 14”
inside dimensions. While the Sikaflex
was curing, I clamped the 2x3 frame to the roof valleys from underneath. Then I went up to the roof and fastened it
using 1-1/4” self-tapping sheet metal screws.
Because they were in the valleys, there was only a potential conflict
with the center screw on the front and back of the MaxxAir “Roof Receiving
Flange.” All the other Flange screws
aligned with mesas. As it turns out,
there was no conflict because the flange screws were farther out than where I
placed the frame attachment screws.
After an hour and a half, I put a dab of silicone caulk on
the underside of the sixteen Roof Receiving Flange screw holes and set the
flange into place on the foam rectangle, and into the roof hole. I fastened the flange with the provided
screws. I covered each screw head with
sufficient silicone caulk to prevent any water leakage, as suggested in the
A note on fastening the MaxxFan to the flange: For me, the MaxxFan did not rest deeply enough
into the flange groove for the thread-clip holes to be visible. I had to move the clips so the clip holes
were near the top of the flange holes, set the MaxxFan into place, then gently
press down on the MaxxFan until I could see the upper edge of the clip
hole. Then I angled the screw into place
and straightened it as I screwed it in.
I did this for each of the four MaxxFan mounting screws.
In my opinion, and from my experience with caulk, lap
sealant, and butyl tape, I would never use any of those products for a project
like this. I recommend the Neoprene Foam
Closed Cell tape and Sikaflex 221 sealant.
The foam tape and Sikaflex sealant technique I’ve documented addresses
the potential leak points directly and decisively.
 Be advised, “High Density” is an inconsistent descriptor. First, I purchased a roll of 1/2” x 1/2", and it was much denser than the subsequent foam tapes I got, even though they were from the same company, and all labeled “High Density.” I would really call what I ended up using to be “Medium Density.” In any case, you need to be able to compress the 3/8” tape to at least half its height rather easily between your fingers.
 Previously, I had been hesitant to tighten it down to that point, but that seems to be necessary to get sufficient compression.