回复：想修窗台板，窗框和部分siding

If the rot started, to cover with plastic will only hide the rot (which will continue).

If it's not in a very conspicious place, you can chisel out the rot, treat the wood with wood hardener, then fill the dugout with woodfiller and paint over. This will buy you quite a number of years. If you do regular inspection and protect the wood by mending chipped paint the wood will last through your life time.