I'm obviously not Virgil, but I've got an opinion and a question or two
Opinion: I should think that an acrylic varnish would nicely seal this surface and protect it rather well.
Questions: How do you work with watercolor on a surface like this and blend smoothly or layer more color without getting a "spotty" effect? What substrate do you use under the gesso?
I am curious, can you post a sample of this technique here?