Foam Creature Fabrication

[MerlinPower]

Hi everyone!!!!!
So....to be clear, although I do love comics/anime/conventions....this question is more about creature fabrication.
My friends and I need to create some deco for a street fair and that deco will be the Spacey Whale.
click here for a pic : https://www.kickstarter.com/projects/41 ... ection=asc

So, initially, I was just going to cut out a 2D spacey whale from some lightweight plastic, so we could hang it...but then I marathoned heroes of cosplay and now I want to actually make a 3d one out of L200 or EVA foam. Ideally I would like to make it at least 4 feet long, and I would like to do it without a metal frame (to make it light weight)
I have seen examples on you tube and heroes where....basically they get a 4x8 sheet of foam and then cut out the shapes, form them with a heat gun, and glue them together...which makes a hollow figure.

Anyone know a tutorial or tool to help conceptualize how to create the 3d model?

Thanks all!!!!