One-Part Product For Rotted Window Sill Holes/Areas ?

Hello,
Great Forums and folks.

Have some rotted wood siding and window sills. Small areas pretty much.

It was suggested that I try the Bondo "Putty" the stuff that comes with the hardener.

Probably ny age now, but have had a devil of a time in using it.

Is there any one-part product that I can use to fill in the rotted out
portions of the wood, and then repaint (or possibly if white, just leave) ?

Think I would want/prefer something that sets up "hard," but would a RTV be a good choice for this ?

Any and all suggestions would be most appreciated.

Regards,
Bob

 

You cannot paint over RTV silicone.