If you pull the middle cushion out towards the v-beth, it is supported underneath with a board, with a "y"-shaped pivot board that folds down for the back-half of support. Use the side cushions to fill in the extra space.
I have the same boat (same year, model, etc.) There's a board that slides out to give it support when you pull the middle cushion down. It's a full bed. Our kids argue over who's getting the back bed. It's "a lot" more comfortable than the "kitchen table bed", which is basically a twin sized...
I'm in the process of doing the same on my 2001 340DA. Shaft seals on my boat cost $55 each + labor. Restuffing the rudders is primarily labor. Anyway, I suggest giving Marsch Harbor Marina on Snead Island a call.