can't get it to keep its shape

Good morning-Jetmodeler;   I have read your post and I have to ask you a question. Are you building this ship like a papermodel? The reason is, most papermodels have you NOT gluing the sides of the hull except at the top(main deck) and bottom(bottom hull plate). You can,t build this way in heavier stock unless you do two things. The first is to make sure that ALL your profiles at the deck and bottom are SMOOTH and correct. Second, make sure you contour your pieces BEFORE installing them on the ship.When I do papermodels(Which I think are a lot of interesting fun) I keep a spritz bottle handy and a large spoon.I spritz a little and then shape the part using the spoon.I do this so when the hull is done, unless I,ve made a boo-boo, it looks like a plastic hull.You can,being as how you are using heavier material put a little tab that,s folded at 90 degrees from the frame in the center, equidistant from the deck and bottom.Don,t make it too big.Then just a little spot of ALEENS craft glue should help you get the contour you want.I use this trick on the larger, 1/200 and above papermodels.I find on the smaller ones if I spritz first,form and install, I have to do nothing else. You can form many things this way,and,oh yes you CAN do compound curves this way in plastic, without the spritz of course. Good luck and let us know how you are doing. happy holidays !!!tankerbuilder     p.s. when you use the spoon, put a small piece of thin foam under the piece,it will form better! This means a lot when you need that curve.

Thanks. I think I will try your suggestions.

One alternative to index cards is IBM punch cards.  Very hard to find but not impossible.  One guy sent me a five pound box of them when I paid postage.  These are thin but have a plastic coating that makes them stable with changes in humidity, which may be problem with your index cards. 

Also you may not have enough support behind the stock.  You need ribs and stringers. Maybe you don't have a dense enough structure to hold panel's shape.

When I made the seat for my F2G I made it from paper but after getting it in the shape I wanted I soaked it with thin CA and thin spritzed it with accererater. It worked great like a tiny scale fiberglass sheet.