Getting a Good Seal when Installing a Fresair S6

and the MaxxAir MaxxFan 7000K

Stephen M Golden

Copyright © 21 February 2023


Getting a good seal when installing a Fresair S6 cooling unit and the MaxxAir MaxxFan 7000K on a RAM Promaster roof.

Installing the Fresair S6

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)


Note: This documentation begins with the unit hole already cut and the bolt holes already drilled.


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 report.


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. [1]


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.[2]  This worked.  After multiple rainstorms, snow and ice, there is no more leakage.



Installing the MaxxAir MaxxFan 7000K

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 instructions.


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.

[1] 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.

[2] Previously, I had been hesitant to tighten it down to that point, but that seems to be necessary to get sufficient compression.