I think it would be better to just extend the trade deadline to either mid or end of August. You couldn't just freely trade in the waiver period anyway.
It's possible Zavala goes unclaimed. But Xavier Fernandez, Carlos Perez, take your pick as emergency back up catcher. But I would probably rather lose Gonzalez from the 40-man first.
They have other catchers in the minors they could call up if Grandal or Collins were injured, even Zavala if he clears. Of course, they would then have to make a 40-man move. I think I'd be ok gambling on cutting Zavala from the 40.
I know we need more power but I don't think it would be wrong to acquire him. Grab him (and maybe a rental reliever from Pitt if they have one?) and Marte from Marlins.