Unfortunately, it's your mother's responsibility to pay right now. She is responsible for his stuff only to a reasonable extent - she should put his actual possessions into storage under his name, pay for a month, and give him the information so he can fetch it out. If he doesn't - and he's acting like a constipated toddler right now, so he probably won't - the storage company can (and usually will) sell it.
(The scrap metal? Take all that to a recycling/reclamation facility. Depending on the metals, those can fetch a nice price and thus reimburse your Mom for at least a little of the hassle.)
She should file for an order prohibiting him from bringing any more crap to the property, and that right quickly.
When he's gone, she can also take him to small claims court to try to recoup the costs of evicting and cleaning up after him.

