Saltwater boat will have a galvanized or aluminum trailer, painted steel is quick death.
Saltwater boat will not have carpet, and all/any wiring will be sealed and secured, NO open butt connectors anywhere.
Flatbottom will go fairly shallow.
Tunnel hull will go much shallower.
Jet will run extremely shallow.
Airboats don't need water.
Each has it's own merits and negatives, you need to figure out what you really mean by shallow.
Marble Falls/Seadrift TX