i have my old single player i want to play it with my frendis so i cant becouse it example.rgd i tried to put example.demp but they told my faild to load save:corrupted

Since DEMP, the multiplayer mod, isn't created nor supported by Raft Developers, you will have to ask the developer of DEMP

Even the DEMP files don't save onto the next time we play.... When is the next update?