I have a Class C E-450 and there is not much in the way of undercoating. I thought of professional undercoating but there is a rat nest of wiring running all under the coach. I don't want undercoating all over it in case I need to repair something electrical later.
The Flex Seal idea is a good one.
Cleaning up the wiring mess under the coach is on my (long) list but I think I'll add using some Flex Seal to protect as much as I can on my own makes more sense.
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