I have a friend that receives many different chemicals in containers on heavy duty pallets. They always have spilled/splashed stains of different colors on them. Some of the chemicals are not dangerous some are at least questionable. Be selective in the pallets you choose.
I don't recall ever reading about the use of the plastic milk crates or the plastic carriers that bread and buns are delivered in. Anyone ever tried those? I do remember when Bruce Condello built BG condos out of that 4" black tubing. Maybe someone that is capable could dig up that thread, it had some good pics with it.

Do nature a favor, spay/neuter your pets and any weird friends or relatives.