If you want a smooth exterior skin, you don't use through-hull fasteners at all. You epoxy tabs (small pieces of wood) to the inside of the shell and attach cabinets, etc., to the tabs, as Gordon describes. Escape
and a number of other companies do it that way.
If you already have rivets, I suppose you could reset them without the washers and snap caps. I've heard early Bolers were built that way. The river head would still make a small bump on the surface, though. Painted to match, it wouldn't be as noticeable.
I thought about doing that myself, as I'm not thrilled with the appearance or longevity of snap caps in the AZ sun. But Scamp
have been doing it that way for 40 years, and I have to think they know more than I do.