Here is what I'm trying to accomplish.  I design these equipment modules for every truck that my company puts out, but they vary on what equipment and type of truck they are on. I'm looking to streamline that process by making them table driven or something along those lines.  What I want to do is be able to change 3 values and have the design update, along with the drawing and cutlist.  I'm pretty sure that is easy enough to have them driven, but what I also need to do is if the design is over 96" long, a forth upright needs to be inserted and spaced evenly. 

My main question I guess would be is it possible to add that fourth piece in the design and also is it possible to accomplish this with weldments. 

Here's an example of the modules with the 3 values I would need driven. 1. The length  2. The Width  3. The uprights which would be grouped as one