GFCIs do not protect against overload - they protect against electrocution by sensing that the current on the hot and neutral leads are the same. If there is a short to ground (ground fault) the GFCI trips. It will not protect someone that is getting electrocuted between the hot and neutral.

The good news is that a standard GFCI outlet can protect downstream outlets. Look at the wiring instructions that come with the GFCI.

On my boat I have two AC outlet circuits - port and starboard. Each has a GFCI protecting the full string of outlets. There is no need to adapt a GFCI designed to go into a power distribution box.