A simple solution is to mount a smaller chain ring. A 26T should solve most climbing problems, just be prepared to get a chain guide.



The RD gives a range limitation of 16T meaning with a 26T small, you would need to mount a 42T big.
I believe this would be easier than changing the cassette as you have to worry about derailleur limitations.
Don't forget to re-measure chain length
If you are still open, there are several other manufacturers providing touring bikes with lower gearing. Marin Four Corners, Cinelli Hobootleg.
I preferred to build from the frame up, so I could have exactly what I wanted on the bike
Let us know what you decide
Cheers