Heater box question

[Juggernaut]

Can anyone tell me if any sealant or rubber seal was originally used between the heater box and the firewall under the dash? The box has posts at each of the mounting points to space the box out away from the firewall. Just seems there would be a lot of air either blowing into the insulation or out the sides. Also on the engine bay side, was the evaporator housing sealed to the firewall? Any recommendations what to seal it up with? With AC on 1978 K20

 

[Snoots]

I used 'rope-dope'. It's stuff that plumbers use. I put it on both sides, under dash and under hood.
It's been there for over 10 years and still works; no leaks!

 

[PrairieDrifter]

3m stripcaulk.

 

[Juggernaut]

So, strip calk or plumbers rope on both sides. Those are great ideas, never thought of that

 

[PrairieDrifter]

I used some foam tape on the inside with silicone on the corners. Looking back I would have probably used the strip caulk on the inside as well, but the foam tape is working good still and that's what factory used on the inside.

 

[Originalthor]

I used 3m strip caulk on the outer box and 3m double sided foam tape on the inside. That 3m foam tape held like a sun of a gun. Took out all the screws and had to still pry it off. You could also see were it had sucked in more on different spots on the firewall so the extra material helps.
I also put killmat on the back just cause I had it

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