There are some pretty fancy carbon-fiber guitars that are made specifically for outdoor extreme temperatures. And I've played those ukuleles like the Waterman by Kala that can be used as an oar if you get stuck in a boat. But I don't think dulcimers built along those lines would be so simple or inexpensive.
My initial thought is similar to what and have suggested. Get an octave dulcimer. They are no more than 2 feet long and can easily be transported in a small padded case and left beside your desk while you work. Then you just sling it over your shoulder, grab your lunch pail, and have a musical lunch hour. I work from home and still sometimes play one during lunchtime! My wife sometimes takes a shoulder bag to work that could easily hold a purse, a lunch, and an octave dulcimer. You could do the same.
Dusty T., Northern California
As a musician, you have to keep one foot back in the past and one foot forward into the future.
-- Dizzy Gillespie
updated by @dusty-turtle: 03/06/19 08:32:29PM