They can't get out of a tub with a lid if you have the proper clips or fasteners for it. Just the lid itself = easy escape. Add some binder clips or small bungee cords like mine and they're not getting out.

As for a rack, check out those threads and do a search here in the forums for rack building and you should find some great tips. As for me, my 'rack' is a plastic shelving unit from Lowes.