Adding underbelly weather protection, is it safe?

If it was me, I would never use sheet metal. If any of that comes loose while you are driving down the road at 60 MPH, you'll be in a heap of trouble and have a lot of damage.

Why not redo it like all of the new trailers with the insulation held up by what ever that water proof fabric is (don't know the name) that they use.
Then if you need to get at any of the pipes, you just cut out a piece, pull out the insulation and then replace it and use a patch

Guy