I'm not sure the answer to OP's problem is in the chassis fusebox either, but at least he should now be able to get it open.
Would like to know more about "shorted out the house battery." Most of all, I hope the battery-to-coach polarity wasn't reversed. A "short" in automotive usually means the Hot got Grounded, or something in the Hot (like a switch or relay) was bypassed to get a circuit tested or working temporarily.
Reversed Polarity would mean Hot and Ground got reversed. For example the battery cables! If Hot and Ground got reversed, some component like the Converter or anything with a logic board is likely to be damaged. Sometimes there's not just one Hot and one Ground cable at the Battery, so only one needs to be mis-connected to cause problems.
And "Everything dead..." Whole RV? Chassis headlights? Horn won't blow? I find it hard to believe that a House issue killed the Chassis?
Find the House Battery Relay. The one that clicks when you turn the Battery Switch on/off. Some would call it a Solenoid and with a Ford chassis you should see the OEM CHASSIS Starter Relay/Solenoid in the inner passenger side of the engine compartment. Little round guy with two heavy cables held by nuts, and a couple small control wires. Well, two more in a Class C. One is Start Assist. Pushing it connects House and Chassis batteries for emergency jump start. NOT that one. The Third One disconnects HOUSE battery so it doesn't get run down in storage. Find that and see if there's a fuse to its control wiring, and/or a Fuse or Breaker nearby for its input/output.
If God's Your Co-Pilot Move Over, jd
2003 Jayco Escapade 31A on 2002 Ford E450 V10 4R100 218" WB