I had a 1968 camper special with a 4 speed that had granny Low. Then 1,2,3 on the knob.
I don't remember if it was a C20 or C30.
It started life with a 240 straight 6. I installed a 327 in it
It was pretty rust free. Sold it around 1980..
Closed cell insulation might be the key to that system working now.
Back in the day they used blue board and pink board - both of which will absorb moisture like a sponge.
The R-Control white 2 lb density foam.board was probably prohibitively expensive.
You could get the R-Control board...
They had a lot of problems with that years ago.
In astray Foam Magazine, I saw 2 houses that had a spray foam exterior.
One I think in Oregon and the other I think in Arizona. The house in Arizona had an Adobe look.
The house in Oregon was owned by a Foam contractor and he used to mess...
What happens with the cracks?
Something to keep the foam from deteriorating or bugs from eating it?
Years ago I got a high density foam with bug killer mixed in.
There's a guy in Alaska on this Facebook thread, that claims to have a new in box DS4 IP with black pmd mounted.
He didn't say if it was for sale or anything. He just stated that he has one.
The thread is a guy looking for an IP for his 1993
https://www.facebook.com/share/p/16XFnZBuDy/