Personally I would use Melamine for what you are looking to do. It is already sealed except for where you make the cuts (and usually on one edge). Either make sure these exposed edges are pointing out or seal them. The downside to Melamine is it is extrememly heavy (for its size) but with only 5 tubs it shouldn't be that bad. I would put casters on the bottom just so moving it is easier when needed.

How are you going to heat it?

Send some pics our way when done.