You should have enough time to do this if you are using PVA and paper.  I would go and find your local furniture store or motorbike shop.  Not as daft as it sounds, ask if they would save one of their cardboard boxes for you, Bike shops are best as the boxes are large and very robust. 

Use this to draw out the armature for your wave, the advantage of this scale of cardboard is that you can do it in one piece.  If you have corrogated card then you will need two layers cross-plyed. 

Once you have cut out the shape you need layer paper and pva, a couple of layers at time and let dry.  Don't water the pva too much, about 25:75, it makes everything soggy otherwise.  Then keep laminating until you have the weight and toughness you want.  Prime with white emulsion and them paint with your final colours.

http://www.papiermache.co.uk/forum/view … hp?id=1257

It might help.  Good luck, and don't be afraid to use newspaper rather than good paper.  By scrounging around you shouldn't need to buy more than pva and paint
If you are really worried have a look at this thread