Hull strength on A/C's

Can anyone advise on how to strengthen the hulls on the Aircraft Carriers?

Through a couple of recent posts and research, the resistance of most of the WW2 carriers to attack is well documented, but with the exception of VonDos's brilliant RN CV Glorious, most of the carriers drop like flies when attacked.

Privateer has already kindly helped me fix a little problem with the German heavy cruisers, and based on his advice there i've tried strengthening the engine rooms, ammo and fuel bunker areas on the carriers. But it hasn't worked.

A single hit from a heavy cruiser shell ( along with a couple from her smaller guns) sunk the Graf Zeppelin immediately, and the Illustrious/Essex class is no better. The weakness seems to be in the hull.

I don't want to start pm'ing modellers because i know they're almost always busy on new projects for our benefit.

Hence this general post to anyone willing to volunteer the info needed.