A tiny dice tower kit that fits into a 4¾ × 6½" specialty envelope. The bottom can hold four average sized dice but only one can be rolled at a time.
Not recommend to ship by "Heavy Letter", as it would likely break. IF you're willing to take the risk, however, it can be shipped that way.
I don't currently offer an official option for customizing this, but I can fit some text or a small image on the tower uprights if you wanted. Just put it in the order comments. Do not ask for anything complicated by virtue of the lack of space, and all requests cannot include things you do not have permission to use from the owner of the work.