not sure of the width of your cage but you can look for an automotive drain pan to set it in. the square drain pans are funneled so you could just set it in your drain system with the cage on top.
how long is your uvb bulb?
My first female veiled did this when I got her, and she had parasites, so a vet check might be a good idea.
My current chams eat mediums and are about the same size you mentioned yours is.
Maybe a pic might be able to help the senior members with a diag.