Don't know how big of a help this is, but I was recommended Aqua Mix Grout Sealer. I haven't used it as I haven't started building the enclosure yet, but it is what I plan to use. I provided a link where you can read more about it. Hope I helped.
P.S. If you don't feel like going to the link, here are the major benifits listed:
>Lasts up to 5 years!
>Outperforms silicone sealers
>Repels food, dirt, and grease
>Inhibits mildew and bacteria
>Resists stains
>Easy Maintenance
>Preserves beautifully
>A single gallon will cover 400 to 1200 square feet depending on size and porosity of the grout joint, as well as temperature and method of application.
Aqua Mix Info
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