I haven't one bit of experience with the type of hills you are talking about...however, I did own (2) Catrikes for several years and rode them extensively around my local area. It's REALLY flat in comparison to what you are talking about, but lots of what I would call rollers around. Short distance steep (to me) hills that my personal conditioning and physical issues caused to make unrideable.
To start the bikes had triple front and can't recall, whatever the stock selection on the back was. I opted to change the rear cassette out to a lower gear inch range and it still wasn't enough. I added a SRAM internally geared hub with a low, medium, and high setting on top of that. I ended up with gear inches such that pedaling at ~60RPM resulted in going all of about 2MPH. It made where I could have crawled up a vertical with the thing so long as I could keep rear wheel traction. The wife and I both appreciated it greatly. It ended up not being so much an issue of conditioning as patience.
I understand that in addition to that, you can add a "mountain drive" style crank system that has the ability to lower your gear inches even more. I would imagine that it would be possible to get an even lower speed at RPM with that setup.
Something else to keep in mind, while on a tangent about trikes. The musculature required for riding a bent/trike is completely different than riding a DF. People call it "bent legs". I would highly suggest you give yourself a good few months of dedicated riding on one before setting out on a journey.