Last summer toward the end of my summer trip, I purchased a carrier shelf for the back of my C with the intention of carrying two plastic storage boxes - one containing my dump stuff and the other miscellaneous. To make a long story short, the shelf rides just above the exhaust pipe and the storage box closest to it melted and was probably close to catching fire. I had a small can of pink spray paint in the miscellaneous box and it exploded. I heard the noise (also a trucker had just passed me flashing his lights and waving - I thought he was flirting) and turned off onto a side road as soon as possible. Parked in a farmer's drive way and after waiting for his great Dane to lose interest in me, got out to check out the damage. What a mess - melted plastic and pink paint all over everything. The whole bottom of the storage box was melted. I pried it loose from the shelf and set it off to the side of the driveway with most of the miscellaneous contents. Saved a couple tools but that was all. Just glad it wasn't the box with the dump stuff in it. Anyway, I left a note for the farmer apologizing for leaving my trash but I couldn't take it with me. Signed only my first name. LOL Haven't decided if I will put an extension on the shelf to get it farther from the exhaust pipe or have something done with the exhaust pipe. Still too nervous about the whole thing to make a decision. Sure missed my DH on that one!
So the moral of this story is - don't add anything to your RV that comes too close to your exhaust pipe.