NIVA Jeeps are good work horses. They are built for that reason and only for that i.e. work hard and not breaking down!!
However, I have towed boats from the UK to Greece many times (more or less every other summer) and the jeep I will use is a DAIHATSY 4-Track 2.8 TDL, 1993 model (got it from new) with about 120000 miles on the cock right now.
Last year I towed the 7 mtr Falcon from the UK to Greece with the same Jeep, went through France and the Alps with two stops (one at Chalons de Champagne and one at Chamberi) and then via the Tunnel de Frejus to Italy via Torino and Bologna straight to Ancona where I caught the ferry.
That particular jeep did the run without ANY PROBLEMS. This jeep has done all the runs to Greece since I bought it (except one year). Attached a photo from last year on the SuperFast ferry from Ancona to Patras.
I also have a Range Rover 1978 model in Greece. That jeep (and old lady with 20000 miles) and 4 gears goes like a dream (although a little bit noisy). Drove it to Greece 6-7 years ago towing an Osprey back then if I remember correctly.
Sold the boat a year later but kept the jeep.
This jeep is like a tank goes anywhere, any time, any day and tows and pulls anything you through at it.
I really have a lot of respect for the old Range Rovers (I guess this is why farmers still use them in the UK).