Huck Finn's raft is described as having a wigwam on it for sleeping in, a light, a place for a fire. Jim had built both the firebox and the wigwam as places to keep them warm, and him particularly out of sight if necessary during the day. The raft itself had a steering oar and a signal lantern.
Jim took up some of the top planks of the raft and built a snug wigwam to get under in blazing weather and rainy, and to keep the things dry. Jim made a floor for the wigwam, and raised it a foot or more above the level of the raft, so now the blankets and all the traps was out of reach of steamboat waves. Right in the middle of the wigwam we made a layer of dirt about five or six inches deep with a frame around it for to hold it to its place; this was to build a fire on in sloppy weather or chilly; the wigwam would keep it from being seen. We made an extra steering-oar, too, because one of the others might get broke on a snag or something. We fixed up a short forked stick to hang the old lantern on, because we must always light the lantern whenever we see a steamboat coming down-stream.
This information is pretty specific and important if you are trying to build a replica or draw the actual image of their raft. Most significantly, this description of the raft gives readers the extent to which Jim and Huck went in order to survive as well as keep Jim hidden. It probably took the brains of both the older, but uneducated man, as well as the sharp 11 or 12-year-old to consider every feature of the raft that would be necessary.