I agree making things out of card board is a trial and error thing and does take real skill, Ive been making everything out of cardboard since I was a kid but now with the discovery of pep, clay molding casting its a whole new world and looks way better. so If I were you blueteamdillan just starting out I would use the pep and just practice, practice, practice.
check out my cardboard stuff on timecon.deviantart.com everything on there is cardboard so please dont ask me what it is made of