Editing Item description

When I create an invoice and I choose an item, I cannot edit the description directly from the invoice. As we are renting equipment, we need to be able to enter a short description on the rental number of days, date, and other relevant details as they differ on each invoice.
I can do it in Notes, but the notes are for the whole invoice, not just this item. (along with the rental there are other services we provide like shipping in the same invoice)