Before working on trailer’s interior layout, it is important to determine the outer shape of the trailer. The curves at the front and the rear of a canned ham shape affect the interior floor space. This is one area where I chose aesthetics over functionality. Functionally, it would be much easier if the walls at the front and rear of the trailer were perpendicular to the floor (meaning no curve where they meet the floor). It would make construction slightly easier and it would give additional floor space but in my opinion it destroys the stylish looks of the canned ham shape.
This image above shows how the curves in the front and rear of the trailer reduce the length of the floor. I chose 12 feet as the maximum length of the trailer body. It was just a guess at the smallest size body that would fit the essential items. The floor area without a curve at the bottom measures 144″ by 79″. With the curves it is reduced to 127.5″ by 79″. That is a 16.5 inch difference. The layout helps to make up for that by putting the bed and dinette at opposite ends of the trailer. It will make more sense why that matters when we get to the layout.
How to pick a cabin shape and how to describe it:
It’s not a trivial task to find a pleasant shape. I chose the tried and true method that many designers and artists use which is to borrow from the work or others. I took the shape of a trailer called a “widget” and I lengthened it and made it slightly taller. Here is the geometry definition of my shape.
The shape is made from 2 ellipses and one circle inside a 144″ x 72″’ box.
Let’s start from the left (rear of the trailer) and talk about each one. The red curve is an ellipse and its foci are shown in the red and white circles. The lines between the foci represent the string that will be used to trace out the ellipse.
Next, the pink curve is the semicircle that makes the shape at the top/front of the trailer. Its radius is R37.5 inches and its center is 37.5 inches from the top and front of the box.
The blue curve is the ellipse that makes the shape at the bottom/front of the trailer. The blue and white foci are connected with a string that will be used to trace out the ellipse. This ellipse is modified where it contacts the floor. Instead of making it curve so sharply a straight line is drawn tangent to the outer edge of the wall at the height of the bottom focus point. This is to keep the wall straighter where the wall contacts the floor. I’ve drawn the 2 inch thickness of the ‘roof’ only at the front and the rear of the trailer because the floor length must include the thickness of the roof.
The 127 7/16 inches measurement is how long the floor has to be so that the walls and roof can sit on top of it. I just rounded the 7/16 up to ½ and inch and that is how I got to a 127.5 inch floor length.