Boat interiors often involve unusual shaped interior surfaces so I've found it helpful to use cardboard sheets and wide masking tape to mock up various panels.  Mocking interior spaces up full scale allows you to make decisions prior to building expensive composite panels.  Fortunately for me, my good buddy works at Full Sail Brewery  ( click here to see some tasty beers  ) and he saves the cardboard sheets that come on pallets full of mysterious beer ingredients.

I use a box cutter and 2 inch wide masking tape to build out interior features just to see If I like the way they will turn out.  If I do, I pull them out, lay them out on my lamination table then build light weight  composite panels using 12 oz glass bonded on both sides of 3/4 inch structural foam sheets.

here are a few panels that I've put into position.  In this case, It was beneficial to do this because I was able to get a feel for how wide the stairway leading down to the starboard hull needs to be. 

 In this photo, I've built a bulkhead that extends down into the port side hull just inside the entrance.  This will serve three purposes. 1  a closet opening will be placed on the end to store foul weather gear just inside the door, 2 it protects the steering cables, 3 an additional closet space is defined down below.   note:  I will create a large opening door which will give me full and easy access to the steering pulleys that are located behind this panel.

starboard side hull looking aft towards the owners cabin