SWMBO and I did it solo with our sidecar. While that's not totally the same as being completely solo/alone, if you are comfortable being in remote areas riding by yourself, I don't see a problem. I had Tony on my notification list for my Spot tracker, so whenever I "checked in" he could track our progress. Just might have to do this trip again, maybe go around the loop counter clockwise this time. We also did about 75% of the Sea to Sierra, but went way too late in the year and go snowed out in the Mt. Lassen area. The huge fires this year kept us from going back and finishing it. We will most likely do that again but also in the opposite direction.