[QuincyAt4M]

I bought a 2021 Montana 3761 FL a few months ago. It has two 15,000 btu Coleman Mach 15s in it with the prep for an additional unit in the kitchen ceiling. During the heatwave we have been having, the temperature outside has been 100-104 F during the day. The temperature in the RV would get up to 84-86 F.
I noticed that when I went into the storage compartments underneath it was very cool in there. I was about to make arrangements to install the third A/C when I had this thought:
The way the 2" aluminum framework is in the top of the storage compartments is perfect to have it shot with 2" closed cell foam insulation. This insulation seals all cracks and is extremely waterproof. Also the never-ending battle of the under-pinning made me think also about having it shot under the RV also. We have it off right now repairing some tank level sensors. I would consider shooting the water-proof foam on the underside, tanks etc. but installing block-outs around the tank heads where the sensors are, installing some 2 inch wiring chases by splitting PVC pipe and bundling wires (without taping together so they can be fished out and in later if need be) and doing the same with any small hoses like tank flushes. Where these block-outs are I would re-install the under-pinning with 2" of the spray foam shot to the back (inside of it).

Now the 64 dollar question.... does anyone know of a reason not to do this? I believe I would not need to install the 3rd AC unit if it was sealed and insulated as described. If it came to it one day to have to dig out a tank to be changed, I'm not opposed to that.

Your technical thoughts are appreciated.

Quincy