Rajul, I'm currently building a 4*60, too. The fuselage is plenty strong enough as designed. I believe some that have fuselage failure perhaps did not glue the fuse properly. The sections behind the wing do not have the bit of extra gluing surface the fuse doublers provide. Simple butt joints between liteply sides do not give CA enough gluing surface to bite good.

The problem is compounded by the fact that the instructions tells the builder simply to rubber band the fuse together and CA. Well, CA needs a tight fit to yield a strong bond, particularly between plywood pieces. Even though Sig does caution the builder to go back with thick CA to form fillets, this to me is not really enough.

What's worse, if you sand to round off the fuselage corners somewhat, you'll end up with even less glue contact area. Bear in mind that bending and torsional moments on the fuse (e.g. from a hard landing) will subject a good amount of shear stress on the butt joints between the four fuselage sides.

I will be using 3/8" and 1/4" tristock to tie the sides together better. Also, CA the fuselage one joint line at a time and press the parts together tight till the CA bond take set. No need to go nuts with reinforcement, just more gluing surfaces for the fuselage structural members to take hold.