The sponsons (two - one on either side of the tank) are the area of the hull sides which protrude directly above the tracks. This area from the inside of the tank is where the ammunition was usually stored.
The problem with Tamiya's M4 series is that the models have a huge hole there. If you look at your Italeri kit, flip it over and look above the tracks, you'll see the sponsons are blanked over. Now, if you do the same with Tamiya's, you'll see right into the hull!
One of the easiest fixes for Tamiya's, is to use
THIS TEMPLATE, It's a PDF, which means that you'll need to download and install
Adobe Reader, before clicking the link above.
HTH
The fix is really only necessary if you plan to have one or more of your hatches open.
