I wasn't going to bother replying to this post again as I think it's one of those problems where unless you know exactly what happened and how it happened as in whether it was the van that tripped or the post that tripped, what was in use at the time of tripping out etc etc, there are so many variables and possibilities that pinpointing the exact cause on here is gonna be difficult, I often have to fault find on cars and caravans as part of my job and often it's not just what the owner says but what they dont say that helps to get to the bottom of things, apologies now for this being a long reply.
It seems to me there have been 2 different things happen, on one occasion the van tripped which gave you some electrics working but not all, as for the trip not resetting again there are 2 possibilities, firstly what ever caused it to trip in the first place is still present so as soon as you flick it up it just trips out again, also I have found in the past that when a switch trips in my house which will happen on my lighting circuit when a bulb blows, you can't simply push it back up but first have to take it further down and then it will allow the switch to be reset.
Then there was the time your electrics went but you say there was none of the switches tripped in the van, are you aware there is a trip switch also on the supply post and if so did you check to see if that was tripped? The post tripping out would give you the scenario of the battery going flat and certain things working until such time as it had run down with eventually everything packing up once there was no electric from the post to recharge the battery.
When you said the breakers would not reset I assume at some point that they did reset or you would still have no electrics or at least some would not still work if it was only one of the caravan breakers still tripped, so if they eventually reset how did you do it?
Re why sometimes the van trips and other times the post. Hypothetically.
Scenario one. The max you are allowed to use from the post is 10 amps, any more and the supply post will trip, with all the stuff in your caravan switched on you pull 12 amps so the post trips, simple, turn some stuff off and reset post trip.
Scenario 2. Max allowed from post 8 amps, you have two 5 amp breakers on the caravan, one pulling 2 amps and the other pulling 6, the post won't trip as you haven't exceeded the 8 max but one of the van breakers will because you have exceeded the 5 for that circuit, that leaves your other circuit still running so you have partial electrics to your van and were then back to why the breaker would not reset, I can definitely say that with a breaker it is sometimes required that before you can move it to the up/reset position you have to push it all the way down before it will allow you to do it.
As I said I think it pretty impossible to get to the bottom of this completely and all we can do is try to imagine various what if situations and then make a guess at it, another big variable is how sharp is the original poster re electrics and then trying to work out what we don't know.
Anyway I've rambled long enough so best of luck in sorting your problem if in fact you even have a problem at all.
BP