Here's what they told me about valve stem requirements. One forum member told me there is some sort of mandatory requirement when replacing them, etc.
Rubber stems is for cars and normal trucks
Hard plastic stems for heavier trucks.
Don't know the weight specs involved but I was told they should have NEVER put rubber valve stems on my MH tire
I haven't looked at new MH's for awhile but I wonder what they are putting on the newer Class C's and/or what tire shops (like the idiot one I went to) are putting on when a tire is repaired. Based on what happened to me I'd check what is on your MH tires!
I was driving long hours on the road into Houston in 112 degrees and the valve stems were literally melting in half.
For what we pay for these coaches you'd think they would COME WITH steel valve stems. :R