Chewing on bars is an act of boredom and fustration. He’s mad because he’s being confined! Domestic rabbits get all the calories they need from hay, pellets and greens just given to them from their humans so try hand feeding veg or putting it in a forage box with straw and hay so e has to look for it, using a treatball for his pellets to stop him eating all of them at once and making him spend time getting his food. Dont make it harder to get hay or impossible to get his food out but this may help make him spend more time playing and foraging and less time chewing!
Suri chews her pen bars when I leave her after petting, she gets real bad and goes bunny phyco on them! Remeber naturally bunnies are more active at dawn and dusk (when their usually put in their pens/hutches/cages) so this can be a little fustrating at times
http://www.therabbithouse.com/…bbit-toys/
this toy usually keeps my buns more than occupied and costs nothing to make. I use a few more of these on the blog. They both literally chuck these around and do a few binkies when they get their pellets out!
Hope this helps!