RE: flimsy motor box
Chewy ... they are usually strong enough for our usual flying but if you want to fly hard 3D it can break, its been known to do so in some top brands. An unbalanced spinner will also contribute to motor box failure. What you can do is to use some balsa tri stock to reinforce the box to firewall. Then maybe some bracing for the box itself. I like that Extreme Flight did with its new 47" Extra 300 XP. They use CF tubes to secure it. Have a look at the attached picture, its a great simple solution.