Welcome to the forum.
Obviously there are no right or wrong answers here. Only you know what you expect or require for your equipment type or style of camping.
You didn't note trailer style, or if you already have generator prep installed which is an addition expense?
https://www.generatorjoe.net/html/portablerv.html
https://www.generatorjoe.net/rv-gene...ators-by-onan/
DIY is not rocket science but requires skills.
Using these boards for yrs. it's obvious no two people have the same wants or needs concerning aux. power options.
We found the Onan option worked well on our last trailer and did carry somewhat to the bottom line on resale. We opted for the same on current trailer, although we do not run a lot of hrs. on it as some might. I prefer not to require an additional fuel, already having ample LPG, Diesel not economically practical. We like the convenience, security, it's rather quiet and is operable underway. Other areas of storage mentioned are also in use (truck bed, trailer receiver / cargo carrier) con: cost.
Any of your options seems workable, and we have witnessed all of them.
2) I've seen the shore power plug right around the corner plugin to generator. 3) I've seen a 30 / 50 A receptacle, bulkhead shore power fitting mounted right there under the pin, neat as can be.
Research is a good thing. Best of luck.