How to repair plastic bottom side sheating

For water line being outside is odd, and for "hot water line" this would be very odd. Coroplast of the "covered underbelly" - I have it in my travel trailer - does nothing for protecting from cold. There are several big openings around the tees and other fittings in that coroplast. Only short sections of water pipes in my rig are outside, for drainage. I stand corrected - there exist not-so-smart designs in RV.

Making coroplast "look neat again"? Like somebody can see it :)... I would staple or rivet a piece of same coroplast over. Sticky tape will work, but they tend not to last long, especially in hot climate.