Chewing on pen

Ever since I've adopted and bonded my new rabbit to my other rabbit, I've had to switch to a bigger cage, such as a puppy pen. My male has always chewed on his cage, but now it seems like he chews on the pen more. Even when the door is open and he has free range to the apartment, he'll go back into the cage and chew or just chew from the outside. I don't get it. Does anyone know why he may do this? Also, my female rabbit is extremely clever and is started to lift the cage up. She learned how to open the pen door so now I know I have to latch the pen instead of just closing it. Any suggestions would be great. Still debating on building a multilevel for them.

could be boredom? do they have a nice amount of toys?

Sounds like boredom. Buy some wood blocks made for small pets or use pesticide free apple branches if that's available where you live. Make sure to feed plenty of hay and fresh vegetables.

i have the same problem .... i just try to key them busy w/ whatever i can find as in chew toy(s)

even if your not there, they need some kind of activities =)

I have an apple tree, I weave some sticks between the wires and Andy will chew on those instead of the cage, you could use any rabbit safe stick that bends slightly