Okay i don't know much about the actual way to do what needs to be done but ill give you a run down of what needs to happen. What you need to do is break the model apart and put it into separate files ie, head, torso, pelvis, L shoulder, R shoulder and so on and so forth. This includes things like weapons and backpack items that can be removed from the main frame of the Gundam. Then you need to make sure all the pieces are straight up and down on the Y and X axis so when i open them in Pepakura they are not tilted and then it is almost impossible to get a dimension from it. After you get that done send me the broken down files with them all labeled and ill let you know what needs to be done from there. If you are breaking it down and you see in a piece there is an unnecessary wall or an opening that shouldn't be there take care of those and make it look nice and neat and smooth.