Wow!! Some things aren't completely unreasonable... others... wow!
I've found numerous items installed, wired or mounted backwards, loosely or otherwise incorrectly. Newmar is a great manufacturer - one of the best and I love the people that work there and the overall quality they produce compared to other brands. But, they are not without fault (otherwise, we would have problem-free coaches from the get-go, what a dream that would be!)
I do believe the manufacturer KNOWS best -- they did design, build or otherwise procure the product afterall. That doesn't mean the manufacturer DOES best. I don't subscribe to the practice of driving cross-country for oil changes, routine maintenance ... or anything outside of structural issues, really. I certainly don't fault those that do (and recognize some just go because the people are so nice,) but I don't believe ANYONE on this earth will care as much about working on my coach (or any other vehicle in my "fleet") as I do.
I have a fluid exchanger, air tools, oil drains and dispensers, a room with nothing but spare parts, filters, etc. and a plethora of other tools and equipment to resolve just about anything that could arise with the coach or other vehicles, so maybe I'm spoiled and would feel differently if I only had a tacklebox full of tools and limited experience at my disposal (electrical is my weakness.)
If you have the physical capability to do your own maintenance, I'd encourage you to learn and try it. It may seem intimidating at first, but provided you follow procedure, it's not difficult and very rewarding. You know exactly what goes in and comes out of your coach, with 100% certainty. For me, maintenance is more exciting than Maxim Magazine.
The only thing I don't do myself is alignments. I'm very lucky to have a Spartan Chassis (albeit firetruck) shop that puts up with my OCPD. I drive it on the alignment rack, go with them in the pit (I adjust the ride height at that time, since it is unbelievably easier that way) let them make their adjustments and pull it back off the rack. That way, I'm still part of literally everything that gets turned, screwed, adjusted, replaced or otherwise touched. It's an OCPD thing. :(
Bottom line: in June, I did everything on both of those lists (that applies to my coach anyway) - including: complete Allison filter and Transynd fluid change (my cost was $400) and a two stage menzerna paint polish and zaino sealant. Total cost was under $1300 (a portion of that was just Transynd) and took 3 days total (1.5 of that was spent doing the multi-stage polishing and waxing/sealing.) According to that list, it would have cost me almost $6k!
To each his own... I love Newmar, but it's not a $6k and a trip to Indiana kind of love.