Looking for websites, exchanges etc where people who have created or substantially modified outdoor technology for their own purposes share it, preferably in enough detail to allow others to comment on its safety and function and ideally create it for themselves. Is there a way to pose or tag questions on outdoors.stackexchange to facilitate this? Are there other preferable sites?
Try /r/bushcraft on Reddit. A lot of that is discussion of shelters, fires, and knives, but making and mods do come up.
Most outdoors people seem to separate their outdoor life from there life in civilization. They expect to buy stuff that just works.
Some of the survivalist subreddits, and web forums have sections on long term stays where they have to fix/improvise stuff.
You may want to flesh out your question with a series of examples, or turn it into a series of more specific questions:
E.g. "Where can I find good instructions on building a lightweight portable twig fired rocket stove"
"How can I easily make a waterproof shelter tarp?"
"how can I modify a backpack so that I can carry out a dead deer?"
"I ripped the sole off by boot. How can I improvise footwear in the bush?"
Some of the homesteading/back to the land sites also do well. Mother Earth News has lots of various how-to articles.
These two are not "the great outdoors" in the recreational sense, but more of a "I'm out in the weather all day every day" sense.