So far they've been great. I've got probably 80 hours on the long tail, and I have no idea how many are on the surface drive, it's at least double. No issues yet. That being said, I've realized since I got it it's pretty heavy for it power output. The vanguard 23hp v-twin is about the same weight.
I've got the same plans this summer. Google Earth is a lifesaver for finding these little islands. I've got one lined up that's only about 20' wide and 50' long, and another that's 40acres and only accessable by boat. Going to make two trips to the big island so I can get all the camping gear in one trip, (2) mini bikes on the next load.