One thing to keep in mind is after a while, the tubs sag, especially if you have a decent number of rats in each tub. Sagging brings the front and back of the tub down, so that gap may double in size.
I had this exact problem in my growout rack. I had to place support under the tubs to eliminate the sagging. I do not have this problem in my breeder tubs, where I never have more than 3 adult rats at a time (I separate pregnant moms).
Also, with a gap that size, you're almost guaranteed chewouts. If the rats can get their teeth on the curve of the tub, they will chew a hole. I had chewouts with a gap much smaller than that. I resorted to riviting 1/4" hardware cloth around the top of my bins, which has 100% eliminated chewouts.
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