Hindsight being 20/20 the extra 1/4 cab would be nice to allow the seat backs to recline a bit more. In the LN2 models (like ours) the 1 1/4 cabs seem to be pretty rare and I am not sure, but the chassis might be the same length (so smaller habitat, which I would probably not want). One of the trade offs with these trucks is overall length, and since North American forest roads are mainly traveled by Jeeps/Pickups turn arounds are harder if needed. If an 1120 and 1124 were side by side with identical specs I would choose the 1124 hands down. It is around $5k to upgrade our 1120 to 1124 engine specs and we may do it down the road.
The truck pictured looks to be an 1824. I don't think this is an LN2 (though that is not really important, but although a "24" might not be the OM366LA inline 6). The thing that drove us to an 1120 was the slightly uprated engine (which can be uprated to 240hp) over a 1017 (which is a great truck). Not sure if it is a big deal as I have never even seen a 1017, just read in some internet "research" prior to buying that some owners wished for more power. I can say that I also wish for more power as the standard 5 speed has rather long ratios so up shifting going uphill is tricky. One thing to think about is final weight and the chassis needed. The 1824 might ride a bit harsh with a relatively light load of a composite box on the back. We weigh in right around the 80% mark compared to the GVWR . Not sure how trucks with a lower GVWR end up.
Being that you are all not large people I think the middle seat would work for a number of years. I think the middle jumpseat was mainly for short duration trips, ours was a firetruck so adults rode there. One thing to also think about is the LN2 is actually a smaller cab than a 1017. Maybe a 1017 would give you a bit more space while still allowing the same sized cab.
One thing to also think about is fuel MPG and which engine. MB has heaps of different engines. I settled on the inline 6 variants do to the reported MPG over some of the larger displacement engines. Plus I wanted a turbo'd engine as I read they operate better at elevation than a NA engine (once again just book/internet reading, no practical experience).
Here is a picture of our cab with the middle seat before we did the cab refurb
Guess the moral of my story, try and get a truck as close to what your final specs require (engine power, MPG, size and 80% weight rating, ride quality and the need for cab AC, ) as changes after the fact, although possible, are costly and time consuming. Oh, one final thing. Being Canadian you might also be able to get an Atego, the slightly more modern replacement for our truck. If we had that option I would have looked into that closely. The one below might be a bit too new (fuel requirements) but is an example. The Bimobil we met up with was an Atego 1126 AF.
Einsatzfahrzeug: Mercedes-Benz Atego 1126 AF - Rosenbauer - LF 10/6 (a.D.) - Mercedes-Benz Atego 1126 AF - Rosenbauer - LF 10/6, Kennzeichen: MST-FF 13, Klassifizierung: Löschgruppenfahrzeug, Hersteller: Mercedes-Benz, Modell: Atego 1126 AF, Auf-/Ausbauhersteller: Rosenbauer, Ausrüster: Rauwers...
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