Thank you LrdSatyr8.
There are no internal structures in this model, just the thickness of the card is enough to support and strengthen it. If you were talking about a section that has a large internal space like a ship's hull or an aircraft fuselage, then internal structures would be required. I have a 4' figurine project that I built as an experiment and she supports herself quite fine. ( Note to self: half to get back to that someday and finish her. ;D )
I have models that are 10 yrs old and still perfectly fine. Some people do coat their builds with clear lacquer to help keep them clean ( finger oils, dirt and dust ) and to give the appearance of a harder, more shiny surface. I have not used this method as of yet. Water is the enemy of the inks. I have not heard of any problems of running from the use of spray lacquer on a model.
Jim