first, be sure you have all the parts, then prime the wood before you assemble it and it would be a good idea to add some wood glue for extra strength and support as you assemble.? If the sides do not slide down easily don't cut the boards, take a bar of soap and scrape it on the raw wood edge for easy sliding.? Then when assembled paint with a good outdoor paint inside and out.? You are not going to have to fill the entire thing with dirt, that will just make it heavy and rot the wood.? Try adding Styrofoam blocks or other light weight filler in the bottom to use up the extra space. We decided to make it shorter so we cut a few inches of the legs before assembly, so the soft wood is an advantage.