I had the opportunity to watch three different kit-built CG Ultimates "in action" before I began building mine. All three suffered broken fuselage sides above the lower wing saddle on less than perfect landings.

So I glued those cut-outs in place, and mine never broke; even after a few hard landings. YMMV.

Be aware that this airplane has the gliding characteristics of a cinder block. Once the engine quits, it is coming down in a hurry. So get the nose down and keep your speed up. If you can't make the runway, get it low, pick your spot, and pancake it in. Just don't slow it down until you're inches from the ground.
I found all this out the hard way, due to one of those miserable Dubro fueling valves that kept sticking. Fortunately, I never did any serious damage to the model, and once I got rid of that stupid valve, I never had another flame-out.

No doubt some will chime in here that their model glided okay and
they never had a problem with the valve. Fine. My airplane weighed just over 9.5#, so it wasn't a lead sled. And I'm not the only one who has had bad luck with those fuelers. I'm hoping the new Slim-Line device is as good as they claim.

Steve