Your "question" seemed a bit lost. Have you used a barrel before?
There are pores in the wood. They will harbor wild bugs if you aren't careful, and can happen to even large breweries that are careful even.
Sanitizer won't penetrate in the pores of the wood, similar to the fact that if you have a plastic fermenter with scratches, it won't always clean it properly and you run the risk of infections.
Soaking a barrel in sanitizer isn't advised, because you'd then have a barrel wetted out with star san.
You could use sodium metabisulphite to treat the barrel after making sure it's wet and sealed, but mostly people do that for wine.
Barrels will just go sour over time, it happens.