Hi everyone!
If you can still read this, I suggest you the 16/35/90 combo. I own the xf 16mm and xf 35mm 1.4 and they are great in most of situations. Furthermore, I have to say that the 16mm is so good and polyvalent that I have almost neglicted the 35mm since I bought the 16mm. If someone want to go on a trip with a single lens, the 16mm could be on top of the list (WR is sure a pro).
I don't own the xf 90mm but I am an happy owner of a tokina at-x 90mm 2.5 (bokina). I just bought this one in order to have a perfect (at leat for me) set for lightweight travels.
IMHO prime lenses are more flexible than zoom lenses due to wider aperture possibilities on the field. I won't bother with heavier zoom (just my opinion and taste).
I used to live on a tropical island so I can say something that might sound crazy here : WR is nice but the other lenses are not made in sugar neither. A non WR lens can be used on a tropical field. What you have to do is to store your gear is a bag when you don't use it (put some silica gel inside), be quick when you swap lenses an avoid to mount a lens every minute. Moreover, you won't have any problem if you are aware of you environment and avoiding windy or dusty moments to dismount your gear,
The best thing to do is to try to anticipate what you are supposed to see every day of your trip and try to mount the most satisfaying lens before going on the field.
I also suggest you to keep some ziplock bags to store your equipment if you have to walk on a heavy rain.
Last suggestion : bring a good polarizer filter with you if you want. It could be usefull for landscape shooting. Polarizer filters have a nice impact on water and foliage scenery.
I hope you will enjoy your trip.
Regards