My bunnies are not big chewers either- if I give them a willow ball or basket it usually takes them weeks or months to destroy it. UNLESS there is treats or another food type motivator involved. Apple branches they have chewed all the bark off within a day or 2- the balsa wood chews (from the BinkyBunny Store) are gone within days since they are fruit flavored, and if there is a treat in the ball they will chew to get it out. Cardboard boxes usually last a couple of months and even then they are not destroyed completely- I just want to them to have a cleaner box and reinterest them with variety. They do loves to rip pages out of their phone books though- but a phone book still lasts them months.
I bought my bunnies a Oxbow Timothy Bungalow- Large and noticed the other day that Schroeder made it into a tunnel- removing the back wall. I was surprised since I never saw him working on it- but am happy that he was interested enough to do it.
So it really seems to depend on the bunnies personality- my bunnies do not dig or chew in their free time out either- so they just do not seem to be diggers of chewers. They get enough chewing to wear their evergrowing teeth down on the hay, pellets, veggies and occasional offerings that they do chew.