Guess I will throw in on this, too - in addition to 'all of the above'.... have been full time living in two different trailers for last 11 years. And seen thousands of rv's and talked with hundreds of owners coming through the trailer park I stay at most the of time. Some miscellaneous thoughts...
One constant you can count on is that most of the newer stuff out there is junk - within the last 10 years or more. Rubber roofs on a trailer are guaranteed leak - in NO more than just a few years, if you are lucky enough to get that long. Most new ones have another built in leak - the slide out. Again, a few years, max. Lots of maintenance PLUS the added benefit of getting to bring into the trailer anything that happens to drop onto the roof of the slide out. Rain. Leaves. Branches. Squirrels. Dirt. Ask me how I know. And yes, you can sweep/wash the top off every time you bring the slide in, and go a long ways to 'fixing' that problem.
Dicor is the rubber roof used, and the caulking/sealant used for the most part. Dicor sealant is crap. Guaranteed to fail soon. There are commercial sealants available that are much better. Everywhere you find Dicor, take it off and replace. Sikaflex 1A is one that works. There are other commercial products out there, but I haven't used them yet. It's kinda like the stuff used to fill cracks in sidewalks. Plus it costs less.
https://www.youtube.com/watch?v=C7LIW1Mwpds
NO SILICONE SEALANTS EVER!! RTV is biggest no-no you can ever do anywhere on an RV!! Also, Flex-Seal - doesn't work! Ask me how I know...!
Avoid at all costs, wall construction that has luan plywood glued to the fiberglass layer as outside wall. It is the worst possible wall you can get. When it leaks - not if - the plywood turns to wet toilet paper and is called "delamination". It shows up as large "bubbles" seen on the outside wall. If you want the best shot at being able to use the trailer over time, don't look at ANY trailer that uses luan laminated wall. Filter out all of the trailers that don't use Azdel (google is your friend!), or build like Doubletree/HitchHiker/Teton. Azdel is good. Rubber roofs delaminate ALL the time - another 'when' not 'if' - so look very closely at roof!! The Dicor sealant on any rubber roof - around vents, A/C, anything on roof - is bad after 2 years MAX!! Again, Sikaflex!!
Haven't seen a metal roof used on a newer trailer for a long time, but it is the best. If you can find a "beater" that isn't too bad a shape, and are handy and want a project, put your own aluminum roof on! IF done right, it will last LONG time! Think Airstream, etc... In general, you can find a used project trailer and spend less money and fix it up to be a better trailer than you could ever buy from showroom! (Except for Lance, Doubletree, Hitchhiker, Excel, etc) Side note on Doubletree and Hitchhiker - place I stay had a tornado event 3 years ago - most of the trailers were disassembled, but a few stayed together (even though still totaled due to damage from debris). For rolling down the road, I like the idea of something that will hang together better. Lot's of "how to" videos out there... Small scale stuff, there is a guy called mobiltec that shows some interesting small work stuff. His canned ham projects show construction techniques that are still used a lot today on the cheaper stuff out there - I have 2, 1990's 5'ers that are built just like a 1950's Shasta! (Kit Sportsmaster and a Fleetwood).
Fiberglass tub - yes. ABS tub - no!
Atwood ovens will never get temperature right.
Dual pane windows sound nice, but unless you are gonna do a LOT of winter camping, not worth the hassle. My single panes have been to -18 F (Kit) and while that is miserable place in that trailer, it wouldn't be much better with the dual pain windows! Plus they leak and fog up and are very expensive to fix. Sooner than later. (See what I did there... pane/pain...) Another "ask me" event...
Watch out for the cargo weight - how much stuff you can take with you! You will always want to take more than you think. It always weighs a lot more than you think! Weigh the loaded, ready to go, rig at a truck stop scale! DO NOT EXCEED!!
Tires - always have to change within 5 years, even if only 50 miles on them. They will not stand up and you do NOT want a blow out and the associated damage! Again, ask me how I know. I try to avoid Chinese tires and only use Goodyear Marathon (and yeah, I know, some of them are Chinese made now...) Biggest tire you can get is best. Size, load rating, etc. Nitrogen fill is a gimmick. Why bother with unnecessary expense? Air is "free"...
This guy. Mostly talking about motorhomes, but absolutely applies to trailers, too. He IS telling it like it is. Boils down to buyer beware big time!
https://www.youtube.com/watch?v=IP_u2JR51_Y