Hi Ted,
I have this series of articles saved. O Gauge Outside. I found it very informative reading with the knowledge of other outdoor railroaders included. It's in a high heat and temperature change environment, Arizona, so the lessons learned will certainly be solid in your climate.
It's centered on Atlas' nickel-silver product.
There's another forum member that runs trains on an outdoor layout in California. I don't recall which track that they use. It is a stable layout.
Another has a very nice outdoor layout also, but that may be G-scale.
The obvious part of outdoor rails is that they require cleaning before each run session.
If find something useful on those other layouts, I'll post the links.
I am sure you could gain some track/rail knowledge from some of the 2-rail garden layout folks from the UK. At least one is a member here.