multibox shipping fee

I have a problem and I cannot find a solution, or a plugin to do it.
Sometimes customers want a quantity greater than 1 of a large items. i.e. 6.0” or 7.5” tubes.
These cannot be shipped in a single box and do not fall under the quoted shipping rates for the order.
I want to add a fee for multiple box orders and extra weight orders, based on the quantity of certain heavy and large items ordered.
Thanks
Dave E