Proportioning Valve Problems

Very good :)
I don't think there is anything we do or don't do that causes the interior of these hoses to collapse. Just lack of real rubber from real rubber trees in the material make up.
The heat is in the drum and will wick to lug studs but little to no wicking to the shoe or springs. Glued linings could come apart though. How much heat required to cause seperation goes to the quality of the glue. Riveted linings wont separate completely like glued but would crack and come apart in pieces. well... Old school asbestos linings anyway. Who know what these modern composite linings might do.
I wouldn't worry about these things unless I had used the very least expensive parts the Chinaman had made.