I use 6 inch UPVC orange drain pipe that I got from builders merchant. It comes in 6 meter length so chopped it in half and stuck it in car. Costs about £25.
I use it behind each sofa to stop bunnies chewing wall paper and sofa and they zip through it no problem.
Just wet a towel and push through the pipe as its quite dusty etc inside.
You can buy 90 or 45 degree bends as well if required.