nickthehunter wrote:
It's called "Duct Board"
Clicky
See the problem with "Duct board" in a RV that I circled in red?
1" is the thinnest I seen on that first page of the link.
Unless you can find thinner ductboard than 1" wall it will be useless in a RV ceiling as it would only give about a 1" inside dimension.. That would be like trying to drink your coffee through a coffee stirrer (it can be done but at a cost of efficiency and not worth the hassle).
For duct board to work reasonably, it would have to be very thin, not much more than 1/4" wall which would take 1/2" of the open framing dimension the OP has to work with.
Thin ductboard also has a bad habit of sagging unless it is fully supported which is what the OP is fighting with..
