Will try to google some info about it.
The Victron MPPts have two number like 100/30.
The first one denotes the maximum PV voltage, e.g. 100V . Use Vmax not Vmppt and add some Volts for the cold dazed as STC is measured at 25C.
So for a 100/30 to an assume two panels in series, each with 40V are ok.
The second number e.g. is the max current on battery side, e.g. 30 Amps. With your 1V system a 30 Amp MPPT can charge up to 360 Watt ( 30A * 12V = 360W).
You can do appr. 130% overpaneling. 360*1,3=468W. So an MPPT 100/30 can handle two 200W panels.
You can get detailed prognosis and recommendation with Victron’s online MPPT calculator.
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This is a VERY useful video for this topic. There are a lot videos out there but this one is the best of all. At least from my point of view. It covers basically everything including concrete examples and calculations for series, parallel, series/parallel, and connection of same size and different size solar panels as well. Super useful video.
PS: …but of couse there is no any example of parallel/parallel connection in it.
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There is one case we have not yet considered at all … If you take a 150/35, which is the same size as the 100/50, you’ll be rid of all your worries. You have a more than sufficient starting voltage that starts early and lasts until late.
All modules in series … only 15A to fuse and your cables are 4mm or max. 6mm … then your roof is ready for further adventures.
The 100/50 regulator has been ordered but it really would be the best idea.
I like your creative mind.
Hm…lemme think.
You mean panel nr1, nr2, nr3 and nr4 would be in series? That means 4 x 23.9V and 10.74A.
And a 15A DC isolator?
I am open for any beneficial changes in my system (it’s not a problem to send any products back to amazon but the package didn’t even arrive till now) but I won’t change my 16mm2 cables for sure. That’s not gonna happen.
I drilled everything through already.
it just happens … 
The series connection naturally has a challenge … to connect everything in series.
I have no problem to play with the positioning of the cables on the roof and connect everything into a series (just as shown on your drawing) then close the circle of the series at the roof entry. That’s not a big deal.
But I won’t drill again or replace the roof entry, or the 16mm2 cable from the rooftop till the battery. It will stay like that.
Your kingdom … your rules 
Too big work. Basically restart again everything. No no…I am not wonderwoman. I wish I was. Can’t this 4 panels in series work with a 16mm2 cable?
…nah…to change to a smaller DC isolator, well, I can do that. If necessary.
Can wonderwoman drill holes in motorhomes? She shoots right through the superstructure … a catastrophe
Of course it does … The PV cables are much, much thinner … I estimate 4mm
Only the junction boxes for 16mm are much too big …
a 16mm cable will olso fix into this smaller DC Isolator … i think up to 25mm
Yes, it’s kinda big diameter. But why exactly do I need another box? What is the problem with the one that I have now? You lost me…
I am sure she would say at this point where are now: …ck it!
I have no idea how you drilled where out of the vehicle and whether you have all the connections on the vehicle … You don’t have to replace anything … but if you have to lay new lines … they may be smaller.
Leave everything else as it is …
The main thing is that it is watertight when it rains …
With installing on the roof one more panel it just needs some extra wire organizing…on the roof. Not in the car. That’s fine with me. A 150/30 MPPT is needed, but the question is that the DC isolator that I have (32A) is compatible with all the 4 panels in series?
Sure 32A is more than 15A … But it could be smaller to have a place for the new Mppt 100/30 …
Yeah. But if a new smaller DC isolator can’t handle my 16mm2 cable then then I’d rather find some place for the ‘old’ MPPT than re-do the cables in the car.
Not enough space in the small curtain room 
You’ll manage that …
This DC Isolator for example can handle 16mm for sure …
The way those panels are mounted I’d say you need 4 MPPT controllers, one for the panels #1 and #2 in series, all other panels need their own controller.
Everything else is BS.
We need the higher voltage of the modules in series so that the necessary Mppt voltage is available as early as possible with this poor alignment.
The whole thing is not great, I agree with you. It’s just a motorhome roof and space is at a premium