My little 6.5x7" sketchbook opens to about 7' long and proved to be the perfect size for my glorious hiking trek along the extreme northern tip of Vancouver Island.
Using 90lb watercolour paper I simply cut single fold pages and using 1"x7" spines (folded lenthwise) attached one to the other forming my accordian. I chose to position my paper so the the join was in the inner crease of each double page. This resulted in some pooling of paint (see cabin sketch) but I am fine with this and was pleased with having good flow from one day (double fold) to the next.
Because I had my paper glued into a hardcover book I could easily sketch and paint with a firm surface yet had the option of opening up the odd time I was connecting pictures with the next page.