Bluesea makes a nice USB charger that is hard wired directly to the boat, instead of using a USB charger:
Dual USB Charger Socket - Blue Sea Systems
It is about $20, so about the same price as a cheap 12V socket and cheap 12V USB charger.
It matches the aesthetics of their 12V ports. No one can accidentally walk away with the charger and give you the excuse that none are left. It has a 2.1A port for iPads and a 1A port for cell phones or smaller tablets.
I carry an inverter, but only use it for charging my camera batteries because there is no 12V charger available for them. Everything else on our boat charges via 12V. We don't ever use the shore power in the summer (I do in the winter to keep a dehumidifer running) and have no genset.