That 30 amp fuse is the "main line" protection device for your 12v system, much like the fusible link in the automobile industry that connects the battery to the car's system. Many things can cause it blow...a faulty ground, a worn insulation jacket that allows the hot wire to contact the frame, a voltage surge at the pedestal; any host of possible causes. I use a "surge protector" on my pedestal connection to eliminate that as potential source of that sort of thing happening, but, many people have camped for years without one and had no mishaps. It may have just been a fluke.
When that fuse blows, it effectively isolates the battery from your system to eliminate the possibly of fire. Since your 12v appliances (ignition for your furnace, water heater, lights, etc) are all 12 volt, removing the battery causes them to cease functioning. Even though your converter puts out 12v to run those when connected to shore power, it needs a battery "sense" to work properly (the battery actually supplies the power and the converter keeps the battery charged) since the output from the converter is "unregulated for constant output" (the 12v output varies based on battery charge condition).
All I can suggest is to check your wiring for frays, make sure that the ground cable has a clean and solid connection and carry a spare fuse (you should gather together a "spare fuse kit" with a collection of fuses for each value used in your trailer). If it happens again, and you can't find the direct cause, it may be a faulty converter or a bad wire in a difficult to find spot (they get very creative when they run the cabling systems on travel trailers). At that point it may be time to let a "pro" check the system out...
My 2 cents, your mileage may vary...
2 Cats; J-Lo and Ragamuffin :R
2014 Thor Tuscany 40RX DP
2011 Ram 2500 Longhorn CTD HO
2011 Keystone Cougar 318SAB (now gone)
2008 FunFinder X 210WBS (Sadly gone)