Sight unseen, here goes a wild guess. Try to position everything as close to correct as you can. IF the wood is just too damaged to permanently repair, you may have to cut out a section and replace it. This might best be done one side at a time, starting with the most damaged side(or top/bottom). Try to tack the pieces in places straight with CA temporarily, trying to get the plane straight. Straight is important at this point, pretty is not. Figure out how much(as little as possible) must be removed from the first side and remove it carefully. Then using fresh wood, fashion a replacement piece. You may want to put small doublers over the seams on the inside, keep them small and light to avoid making the tail too heavy. Attach one end first and after it sets attach the other. Remember that you can cut access holes in the other panels as you are going to replace them anyway. When the first "side" is repaired try doing the same to the opposite side. Continue with the remaining sides and recover. Nobody said this will be easy but it probably can be done. It's usually easier to work on these with all of the "stuff" out of them. If the sides or bottom is FLAT, then a table makes a good fixture for getting things straight.
Waiting on the pictures now.[:@