The obvious differences between US and Euro customs, usage, and conditions make it difficult for me to comment usefully on much, but a couple of items may be helpful.
There has been some mentioned of the frequency with which towed units end up in the ditch. When I purchased my current 26 foot trailer, my dealer advised that I did not need an accessory "sway control" device. HE LIED.
For those using "receiver hitches" small trailers, and expecially the popups that are not taller than the towing vehicle usually don't give much trouble, provided that the towing vehicle is actually suitable for the towing task. If is my "discovered" opinion that any towed vehicle large enough to need a "load sharing" or "equalizer" receiver hitch, or that is taller than the towing vehicle, should have at least a "friction antisway device." This is generally about a $100 to $150 add-on. Even if the trailer tows easily in normal conditions, there will be times when wind, road camber, or other conditions will make it respond "unpredictably" and perhaps uncontrollably.
Different rules apply to the "fifth wheel" hitches that are common here, but it's my impression that those are less common in Europe(?).
For "self-contained" units of any kind:
The most common major failure I've seen or heard frequent reports on, especially for smaller units, is with the built-in refrigerators commonly used. The common propane or multi-power kind invariably operate on a convection cycle that will "stall" if the refrigerator is operated for too long in an unlevel position. If the cycle stalls, the refrigerator will self-destruct. Replacement "cores" for the smaller ones start at close to $1,000 (US) so it is good practice to be careful.
The sensitivity of a given unit to this failure mode seems to be directly related to the height of the convection stack (and size of the refrigerator). In a camper that you can stand up and walk around in comfortably, you'll likely have a tall enough convection column to be safe if the camper "feels level" when you walk around inside. In popups or van conversions, you likely have a very short convection path, 3 feet or less, and a correspondingly small "reserve" volume of refrigerant fluid, and should use at least a small "bubble" level to get accurately leveled before running the refrigerator for more than a very few hours (1 or 2, not 5 or 10) in one place.
About 15% to 20% of popups more than a couple of years old that show up at our biggest festival have replaced their original refrigerator with a "household" electric (AC) only unit. It's not as nice as the original, and only runs where/when you can plug in, but it's a lot cheaper. Another 20% just "don't have a refrigerator any more."