Hey @Dieseldonkey that was actually my first thought and I remembered that you had done this with your bamboo. But I sadly don't have a go to spray shop that I trust and also it would have to be the whole of the units and not just the tops.What about clear auto paint lacquer. My local go to spray shop did the bamboo table and work tops with it. Seems very durable. Designed for plastic bumpers, so has a bit of give in it if the wood expands/shrinks a bit.
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The van is going to get more abuse internally than normal perhaps as it will have windsurf kit chucked in and out so wold probably need to be quite easily refurbished.
Although the way I am building it templating new worktops with the router every few years would be pretty easy.
Simple acrylic varnish might be the way ahead here unless I can find an oil product that stays clear