My rats and ASF's are all housed in the mortar tub racks. I've not had any issues with chewing or escapes with either species. Any biters or chewers get fed off as soon as I find one and thus far I've not had any issues with them chewing or escaping. The only change I made to my ASF rack was to tighten the spacing between the tub lip and the rails, plus using 1/4" screen instead of 1/2" screen/hardware cloth on the top. I feed mine fresh veggies and fruits along with bird seed and lab block, plus I give them cardboard tubes and boxes to chew on, along with small chunks of pine lumber (non-treated). Mine don't have wheels or anything and are breeding and feeding fine with no issues as far as chewing or anything of that nature. I cut masonry bricks in half and put those in the tub to let the adults reach the water spouts since I use a gravity system with them rather than bottles. The one issue with mine is the spacing on the rails that hold the tub lips: they're fairly tight so it's a bit of pain to open the tubs but they've started wearing a groove from where the hardware cloth has worn down the plastic so they open more easily than what they did when I first built it. Otherwise it works great and is nearly identical to my racks for my Norways, with the exception of the bricks to give them some height to get at the water.