I use pond liner to protect the boot sides and backs for the seats, but its protection from fishing equipment and dumpit stuff, so might not be suitable for dogs.
I looked myself for a suitable liner, but as you say none actually covered everything I wanted at the right price. I use a piece of carpet to protect the boot tucked under the truck liner.
Aldi sell a cheap rubber type covering in black occasionally, I bought two and find them useful for the dump pit run, but not I would thing dog proof, I suppose it depends on how active your dog is.