Which evil round parts are you talking about? If you're talking about the barrels, try rubbing the sheet over the corner of a table to give it some bend. Then, you may want to try using a wooden dowel for support while you glue the barrel closed. Also, don't try glueing all the tabs in the barrels at once. Take it one or two tabs at a time.
Does that help, or are you asking about a different part?
it helps, was talking about that circular knee piece. should stop gluing all them tabs first
*drool* low viz