It's kind of a strange ship, but honestly, that's the fun of it. Pushing beyond the typical pairings can lead to some really creative stories. I once read a piece where the crew gets stuck on a winter island, and Chopper's medical knowledge becomes crucial for their survival in the extreme cold. The author spun this beautiful, platonic-focused plot where Nami, as the navigator responsible for getting them into this mess, feels immense guilt and works tirelessly with Chopper to keep everyone safe. It wasn't romantic at all, but the deep bond of trust and reliance they built felt more meaningful than any forced romance.
If you're going for romance, you almost have to age Chopper up, which is its own can of worms. A popular AU idea is a modern coffee shop or university setting, stripping away the pirate life. Maybe Nami's a stressed economics student and Chopper's a quiet, genius med student who tutors her through a tough biology requirement. The dynamic shifts from caretaker/patient to equals navigating adult life. The slow realization that their friendship means more could be sweet if handled with a light touch, avoiding the ick factor.