Since the fenders unbolt, you have options to buy OEM or aftermarket replacements. But the Tub you pretty much have to cut the rust out to clean rust free metal then weld in new sheet metal, and then grind down the welds, bondo/primer/paint. (Best to have a autobody shop do it.)
I suppose a temporary fix is that you could cut the rust out to clean metal, paint any bare exposed metal, then throw the plastic panel back on to hide it. But fix it right before you ever sell the Jeep.