bicycle seat post plug 30mm

if you have to leave your expensive bicycle out in the rain and snow you will nead to protect the inside of the seat post as well as the rest of the bike from moisture i used to use a plastic tarp over my bike but because it is a trike i cant completely tie the stupid thing down to the bike the wind always blows it off so i have given up on that thought and every month or so i spray the whole bike with wd40 to prevent rust and i mean every thing tires chrome brakes everything i thought that this might impair the braking power but seems that the weather over time removes enough wd40 to make good braking ??

bought a new can of wd40 and now it is silicon based could not find the old stuff i do not know how this is going to affect this process

this bike is about 10 years old now and ben out in the rain and snow for all of that time and still looks as good as the day i purchased it every once in a while i have to take a wire brush to small rust spots but if you keep it as a regular p