I use this in my hutches, it's very cheap, wide enough for big piggies, Stanley is a big lad, it comes in 2m lengths and you can stick carpet to the base for grip using double sided carpet tape.
Wickes Brown Square Line Gutter Length 2m | Wickes.co.uk
Awesome idea using the guttering! How is cortex strong enough for ramps anyway? I would have thought it would bend?