Thx ec121 for your input. I feel that those struts are OK for this plane. It's not a 2Lb foamy one .
Just nothing to do during winter time and I want to make new struts.
I also set a CG around 85mm. Maybe your rattling sound is coming from pushrods? They may vibrate in tubes.

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Kostas1
If you familiar with covering films (Monocote or Ultracote on whatever you used) the covering work is not difficult, but on the initial stage when the ailerons, elevator, rudder and fin are not connected to the fuselage, wings and so on. If the plane is assembled, the covering work is challenging. Some people cover the plane splitting surfaces by small areas. However, seams of one color are visible, and the plane looks like after a repairing work.
Also this particular aircraft has a weak point - side windows. They are permanently glued into the fuselage. You cannot easily remove them during covering work (I unsuccessfully tried)