I am SO glad the rats are okay, that is great news!!
What a relief for you, eh? You should not feel silly about taking them in, as you didn't know whether they were okay or not, so it is a weight off your shoulders to learn they are healthy!
Hopefully Breyer, who uses fabric, will respond to your questions about fabric, as I THINK she clips the corners down somehow? Breyer, was that you, or someone else?
I never really had a problem with my two boy rats, Klausse and Wolfgang, chewing up stuff too bad. At least not the base towels, because I would spread out the fabric and fold it so it matched the width and length of their house base, then by the time I put their litter tray on it, in a corner, and their hidey huts and toys, food dish, etc, all of those things pretty much weighed the toweling/fabric down on its own and it stayed put.
I would throw a few extra flannel or fleece blankies in there, in little piles, for them to cuddle in, or chew on and just for general playing. Rats love to play and nap in cloth blankies!
Also, yes, I liked to line their platforms and shelving with fabric too. I would just fold up the fabric into a rectangle to fit the diameter of the platform. Sometimes the boys would sleep on top of it and other times, they would push it aside and sleep right on the plastic shelves, probably because they felt cool and smooth on their tummies.
I am sure you will get lots more advice on this. Cloth and fleece/flannel fabric are great for keeping zero dust around your babies, for their delicate noses.