I've got two racks that hold sweater box and blanket box sized tubs. I haven't seen any racks that hold two side by side tubs large enough for adult rat/corn snakes.
Check out Animal Plastics
www.animalplastics.com/
and Jason's Jungle
www.jasons-jungle.com/
I don't think sweater boxes are large enough for a single full grown corn snake. I keep my adult rat snakes in blanket boxes. The sweater boxes are a good size for larger hatchlings to yearling snakes though, depending on the species.
Both the racks that I have (from AP and JJ) are well made and very sturdy. The AP comes disassembled but is easy to put together. The JJ is fully assembled (with tubs)and has two strips of flexwatt running down the back so that you can keep snakes that require different temps in a side by side sweaterbox set up (but you'd need two thermostats to do that).
I also have a hatchling rack (and a stand alone large cage)from Boaphile. Here's their link.
www.boaphileplastics.com/rhinoraxx_choices.html
I haven't tried the Rhino Rack yet, though it also seems like a sturdy rack.
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Lora