cjs,
I don't think anyone's own individual idea to improve his bike or trailer or car, for that matter, should be thought of in terms of good or bad. What's good for one person may be bad for another.
The initial question I ask myself when deciding to customize or alter something is; "why am I doing this?". I thought about spray liner but rationalized that the stuff was designed to protect the steel (and when textured keeps stuff from sliding around like things do in a bed liner) inside a pick up truck bed. I didn't want to accomplish that inside my Aluma. I wanted to soften the inside, create a more "hospitable" climate for our gear and stuff, be able to take the bottom layer out to clean if necessary, and remove screws, bolts and wires if the need arose. And be able to replace any damaged section if it was required in the future.
My expectations were exceeded with carpet. I even left a camera inside the trailer and after "rolling around" on the carpet during a mountain ride no harm came to it. I was also really glad to see that the methods and materials I used FAR exceeded the carpet I saw in the "Big Boy" trailers during Wings Over the Smokies.
It's all about personal preferences and best of luck in whatever you use inside your Corona Cart!