Been contemplating a Rohloff hub for my R20 tourer rebuild...... now that would give me enough range when touring.
But as I am SO poor, I will try to make my SA 8 spd work with a chain tensioner and 2 chainrings.

My three R20s are non folding, I can't fault them for carrying heavy loads, there's no flexing.
I admit they are finnicky little so and so's at times with the BB and fork steerer, but that's half the fun of doing it.
Once that's sorted out, they may be a bit heavy, (but a tourer isn't meant to be a light weight bike), they will still outlast all of the modern folders so far mentioned.