I've just bought a nearly-new fiberglass boat. What's the best treatment to protect against blisters in the future?

Protection is always better than cure and it really does make sense to protect a new boat as well as an older craft. We strongly recommend that you use the Interprotect system. This is a multi-coat system of an extremely waterproof epoxy primer specially formulated for this purpose. This system is described in detail in the BPG "how to protect against osmosis" section, where you will find step by step tables for the preparation and application of the system, and how much time you will need to do each stage.