I am also doing a large canvas as mentioned earlier and I am photographing the various stages. Here is a picture of stage 1 - laying down the backgrounds.
"Island" - May 2010 by Ian Ridpath - Step 1
I have laid down the sky and water backgrounds. The water colour is exaggerated and will be softened later on. The sjy is probably as it will be when the apinting is finished - I may add some more cloud detail.