All of the exterior doors were made by Challenger door. They have some wood on the inside and get moisture in there. Then they start to corrode from the inside out.
Warranty- nope
Replacement-Contact Challenger Door. There should be a white label on every door. It will let them know the correct size, color, etc.
Price- I paid $550 for a new entry door with screen and new locks. That included tax and shipping in 2020. Obviously shipping will depend on where you live. I would think the ramp door could get send, but they will be able to tell you.
You would either need to replace them yourself or have an RV shop do the work. Entry door wasn't too bad, haven't tried a ramp door yet.