What your talking about is called Ensolite, or elephant hide. It is difficult to remove, and there is no better replacement. The modern alternative is Reflectex, and hull liner, (rat fur). Not easy to install either.
Ensolite is considered by some, (me) to be the ideal fiberglass trailer liner. It's purpose is mostly to keep the condensation down. It also serves to keep light
from leaking through the fibreglass and to help with the sound of rain hitting the shell.
What do you want to use instead?