
How about a thick piece of carpet offcut, cut to fit the tray? I know what a problem chewing is, I've had one!
I'm about to invest in some Tuffie beds for my two adults and the pup will have one too when she comes out of the crate and can be trusted.
I don't think the plastic Tuffie bed is for mum/pups, they advertise it as an indestructible dog bed for chewers. Very pricey, and not sure about fitting into a crate really.
Tough one! :)