I think you guys are misinterpretting what I am saying. I am saying to foam fill, apply foam in a liquid form and have it expand accurately, it would be tough without a core. I am not saying you cannot ghetto fabulously start gluing in random pieces of sheet foam/upholstery foam/etc. until it fits reasonably well. That can be done with some Barge Glue, and a lot of patience. But, it will never be a 100% fit. I would imagine that hardly needs a tutorial. Simple: take foam, apply adhesive, stick in to suit, repeat as necessary until it fits well enough. Now, filling with expanding polyfoam, that would be quite a tutorial, but an expensive one.
I wish you guys would not take my comments so personally. Every time I offer a response, it seems someone feels injured by it. I am here to help, and offer advice where I can.