TonyB

But then in another video he says the inverter has an overvoltage cutout of 520V. I have my salt-shaker next to me when I watch his videos 😂 

Thank you - Will have a chat with the installer about using two separate strings. Makes a lot of sense.
 

The 250V seems correct as indicated. I would put each string on its own MPPT and you will see the output from each one. This will also allow each one to deliver it's best output during the day. SW will be bad this time of the year. 
@TonyB
You beat me to a reply 😀😀

This creates a 40% drop. 

Yes
 
@TonyB I can see you are doing your homework properly , as it should.👌 As a result , you are coming up with some good and 'nasty' questions. This one I had my head scratching , again !  Never given thought to this before , but let us analyze this from reasonably first principals , and see where it takes us , not least to attract guru's on this subject :
1. Logic tells me , and as Mike Holt says , current will flow only if it has a path to return to the source . The source in your case is the Neutral at the inverter , which is anchored to earth via the earth rod near vicinity of the panels.
2. The quality , or the resistance of local earth at the caravan in relation to the earth rod , to me , is neither here nor there.  I mean you have factory floors and large homes , where distances can easily reach 30m and more.  The bottom line is that the caravan local earth may be very low in relation to the earth rod , or it may be very high . Lets look at the implications of both , and for that matter anything in between :
3. If the earth is low , i.e. same as earth rod , that's good , meaning any diversion from live to earth will be well detected and earth leakage at the inverter will trip.
4. if earth at the caravan is high , then the return path to source is compromised , and no current or very little can flow thru you when you touch live. Remember you are lethally shocked  by a current exceeding a certain minimum (say 30mA) . If the earth is  high , that current will not be reached. If the earth is perfect in relation to earth rod , you will be shocked but the 30mA will be drawn , and RCD will trip.
5. This brings me to a question that many people have : why then bond the neutral in the first place ?, just leave it floating , then no one will ever  get shocked !!!! Unfortunately this is not a perfect world , and inadvertent earth leakages between cores and connections and insulation and earth will always be found  , un-deterministic 'bonds' . And many such  small  'bonds' will be in parallel  and will eventually constitute small enough impedance to allow human to get shocked. In this case its best to take one feed from the generator and earth it hard , and let it henceforth be named as Neutral . The remaining feed will henceforth be labelled as Live. Then force upon our beloved ones the deterministic RCD or ELD. 
6. For all these reasons , you need to carry the system earth from the rod , all the way with live and neutral , and install surge protection etc at the caravan , with reference to this system earth.
This is my 2 cents , so I invite members to comment , please because @JohnB needs practical answers . @Modina , @Scorp007 et al.