Placing two shipping containers side by side is a very common thing to do when building with boxes 8ft wide. When building a home involving two units side by side you must remember two things. One, you must seal the two units properly to prevent any water leaks, and two, the foundation must be perfectly level.
During the installation, after the first unit is in place you will need several people helping, with ropes, guiding the second swinging container into its proper place. Once we have the two units side by side we use several industrial vices to squeeze the units together. The protruding corner posts on all shipping containers prevents perfect seal when two units are side by side.
The method we use to create a seal is with roofing cement, thin sheets of metal and welded corner posts. Once the two containers have been set side by side on their foundation then you can begin to weld the units into the foundation and the adjoining corner posts. Before applying the roofing cement you must first install the rolled roof flashing inside and outside the opening. The combination of these three should create a perfect seal.