Hi @PeterM,
We don’t have any near-term plans to sell additional 6"/8" enclosure lengths or end caps. I’d recommend filling out either the “Request a feature” or “Ask a product application question” form on our contact page.
In case it’s relevant, it’s possible to get custom tube lengths for the non-locking series flanges from eplastics.com, which we have a direct product link to from the 6" tube page 
Exciting!
There is some precautionary commentary on dome/lens selection for this kind of application here, from our BGH1 integration.