Sorry... yes they do have waterproof boxes similar to a Pelican case, but it was the cell phone/ PDA/ iPod/ Palm cases that I was pointing out. Not waterproof, but shock and dust resistant at least.
I have not seen iPod/iPhone cases from Otterbox. I've seen some protective cases from Marware. They looked very similar to the Impact Case from Otterbox. I found that they were on the heavy side as rubber they were made of was thick/compact. It might be a problem or not.
Edit: from the OtterBox spec sheet, the Impact case weight is around 17g or 0.6 oz and it's not made out of rubber but silicon