Adding simple sand bags for ballast?

Hi:

I have a sterndrive Bowrider (175 HP) and want some ballast to improve the wake (newbie rider).

I have been checking into Fat Sac, but can one just take some bags of sand and put them in the ski locker etc?

Also, where are the best points to put ballast (Fat Sacs or sand bags) in the boat?

Thanks in advance.

Marshall (Toronto)