Those guys are right.
In answer to your question, I think the best way to make a cardboard template is with strips. Depending on what part of the boat you're trying to make the template for, the strips could be anywhere from about 4" to 12" or so. The photo shows how I did my 1236.
The idea of the strips is that you can position them to follow the inside contours of the boat more easily than larger pieces. Your cuts don't have to be so accurate at this point because you are really just pushing the strips against the sides and then taping them together to make a shape of the whole. It's so much easier then trying to measure the dimensions and transfer the info to the cardboard.
Here's the template for the floor of my 1448.
At the ribs you place the cardboard strip along the side and mark the location and depth of the ribs. You can cut them closely or not but the final shape of the cut can be made by using tape in the same way you'd use the cardboard strips. In other words the tape is used to complete the finished shape over the notches you made for the ribs in the cardboard.
A couple of things to remember when you are doing your figuring. Your template represents the
bottom of the floor. So, if you are using 1/2" material and cut it at 90° to match the template you will end up with a gap at the edge because of the angle of the sides of the boat. When I did mine I used the template to mark the
underside of the floor material. Then I cut at an angle away from the inside of the template making the edges of the cut angled to conform to the angle of the side of the boat (this applies to the sides only - the front and back of the flooring are cut at 90° where they butt against the seats). This makes a better fitting and better looking piece when you're done. Turn the template
upside down when you transfer the shape to the floor material. The top or "up" of the template should be against the underside of the floor material when you trace it.
You can see in this photo how nicely fitted the floor can be if you take your time on the template and take into account the angles of the sides.