I have made up three similar sentences below.
(1) I will be available to volunteer for all of the winter.
(2) I will be available to volunteer all of the winter.
(3) I will be available to volunteer all through the winter.
As a non-native English speaker, I think they all sound okay. However, some of my non-native speaking friends think all of my sentences sound unnatural.
Do they sound OK to native speakers? Please give me your opinion. Thanks a lot for your help.