Wow, lots to consider. Will give due thought when head clears.
Need to get it solid cos I'll be there for a looooong summer this year.
Router is in a square room of glass and plastic built on the back/side of an L shape. Rivetess is in (I think) next door but one - in the wrong direction. He needs his signal strength in other directions cos his computer room is in a shed in the garden. I happen to know these houses are 9" solid redbrick and carry water out of the ground despite being 70" high on the cliff edge. There's a well in his old computer room, and the most powerful dehumidifier couldn't cope with keeping it dry. So, walls are good cages I would think.
As I say, I'll read through again tomorrow - but I'm still at GMT -6 in Tumbleweed town.