While working on my Battlestar Galactica model I came upon a nice inexpensive way of adding strength to parts. I use Berkley Square Wooden Stirrers. These are wooden sticks (13.97cm x 4mm wide x 1mm, $2.99 for 1,000) that are mostly straight, lightweight and easy to work with. You can even use them to stir your coffee! (WOW!) Here's the Galactica's upper bow with stick reinforcements. This is a good example of using the sticks to get straight edges.