Locating framework for rib cage?

[freds]

Hello

I have a 1980 LeMirage that began life as a motor home and in updating the house systems I am considering adding a skylight in the shower.

I currently have the refrigerator out which is on the other side of the wall from the shower; changing it over from absorption to a DC compressor and I can see what looks like a heavy duty attachment point that should be anchored in one of the ribs.

I know my bus has an outer skin, rib cage/foam insulation and inter skin sandwich. Question, how do you go about locating the ribs?

[Gil_J]

Doesn't that illustration show the ribs? If you're trying to find them from the outside of the coach, wait for a humid morning. They will often be clearly visible before the sun hits the skin.

[Joe Camper]

The interior is lined with plywood attach the refrigerator to the plywood it's not going to go nowhere.