Thanks all for your help. I will be taking a brompton for a spin tomorrow and will report back.
Bookishboy, I am willing to spend around 1000 USD (still way less than a car
). I've been living on the boat for quite a while and I am quite aware of the toll on steel and other metals from the overall humidity in the air (and the salt), so I think I should be alright with the necessary repairs and tuning. As for the pannier, it is not necessarily a deal beaker. A nice handlebar bag or something like it could work. Now if it can swallow an Arkel bug whole, it would be even better.