Since you have verified that there is a problem, to avoid blowing/replacing fuses or possibly damaging some wires, I would go a bit different. Before putting power back on anything, I would go through the trailer to any breakers or fuses you can find and flip or remove them.
This will allow you to go back to the first point where power is added and test small sections at a time. It is possible to damage wires if they are overloaded repeatedly, so good idea not to do that!
The automatic breaker sounds like it should reset itself when it cools but check that !
When testing with a meter and checking continuity, be aware that you should not see any continuity from positive to negative side when there is not a load as when you have the breakers or fuses off. That is a good time to check the positive side to see if you see any ground on it! If you see ground on a positive wire when all the breakers and fuses are out, that is a clue! Find and repair that ground before putting power back!
It can be that you have missed a fuse, etc or it can also be a wire that has been damaged like in scraping on metal frame or boxes and that is what is tripping the power.
Fix the cause before putting power back as power on it too often can cause more damage!
On testing the negative/ground side of the circuit, you likely will see ground but that depends on how the circuit is designed.
When you are done testing the first section of wire, finding no continuity to ground on the positive side, try turning on or replacing one breaker or fuse to add one section of additional wiring then test again with the meter to see that you are getting a change.
Depending on what is on that circuit, you will likely begin to see continuity from positive side to ground! Don't let that surprise you as it is normal.
The positive wire goes out, through the fuse, to the wire going to some item in the RV. That item (like a light bulb?) will normally have a connection through it to the ground side. That is a normal good circuit (circle?) But the resistance of that continuity is something to try to judge.
When you check that continuity, the resistance you get will depend on the item it may be feeding. A single light bulb may have little resistance while a motor like a vent fan may show lots more resistance.
What you want to watch for is a positive wire that has really low resistance to ground. That may indicate that the positive wire is shorted to ground before getting to the item is should power!
Just as you mention, the smaller fuses/breakers should trip first if you have a short beyond them! Things are not always like we expect but it sounds like you will find the positive is shorted to ground after the breaker which has smoked but before it gets to the other fuse panel!
That's where cutting all the load off from that second panel will help cut the chase when first testing.
Something like this? Disconnecting as much of the system first and testing each small section as you add it will avoid replacing fuses and/or doing more damage as you go.
I expect it should be a problem between the first breaker and any load centers you have! Guessing! But one place to look carefully is where that first breaker sets and maybe where the main wiring goes out of the box? Any signs of arcing?
But my guesses are bogus if you find different!
We would like to think the smaller breakers would go first but life has a way of tricking us!
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