I've not got my double din screen yet, but that's what the plan is. Some double dins fit the space fine, others are slightly too big for the front dash trim to go over. I think its to do with the design of each individual unit. Some units are designed to sit flush with the dash, others are meant to protrude a little. The ones that protrude will more than likely mean that the dash hole has to be trimmed top or bottom so it slides over the moniter.
My plan is to get the moniter to sit completely flush with the dash, this may mean drilling holes in the side mounting brackets, either in front or behind the existing ones to makes the unit sit further in or further back.