I recommend going to an RV rally (any kind) and asking folks to show areas to inspect on a new trailer. It will help you see what to look for - things like corners that don't line up, and so on.
Yes, most trailers are built the same. Some makes have better reputations, but you can have issues with any. Getting someone who has been through it to walk you around a few units and point out things will go a long way as you start looking to buy.
Small trailers have options with fiberglass shell bodies (casita, escape, etc.). Bigger trailers tend to confine you to the standard build techniques. Also, unlike cars, RVs are more likely to have different issues from the same build period. So, when you narrow down your preferred floor plan, don't just ake the first trailer they walk you to. Check all the trailers on that lot with that floorplan. If they don't look that great, go to another dealer and look at all their trailers with that floorplan.
And remember that many different trailer brands are made by the same company and offer the same floorplan. So check all the trailers in different brands with the same floorplans.
As for water damage, sidecarflip is right. Some due diligence and preventative maintenance goes a long way. I'll add that after the first rain of the season, go out and check your trailer for leaks. Do not put it in storage and forget about it until spring. Even with indoor storage, you can come back to a destroyed trailer. A leak found after one rainfall can be fixed relatively easily for the most part. A leak found after an entire winter of storms is a lost cause without rebuilding.
And remember, indoor storage can have a roof leak, or a fire sprinkler malfunction, etc. Not catching those quickly can do as much damage as leaving it out in a rain. Make regular checks on the trailer when in storage - you'll not only catch water issues, but electrical malfunctions, rodents, insects, theft, and so on.
And yes, plan on maintenance and repair work. Just like when buying a house. Things break. Preventative maintenance is cheaper than repair. And so on.
In the end that part will come down to your personal preferences. Some people love camping/RVing so much that the added effort of maintaining a rig is worth it. Others don't. You'll figure out which one you are after about 1-2 years at the latest.
