Damn if I wasn't gonna make a joke, but thought.."This is what I'd do...'
The biggest issue I see isn't the triple, it's securely attaching the new outlets to the wire as it gets thrashed about.
So why not just get an ugly arse box and hook it directly into the line. (and not use the male plug as pictured) This would give the ability to secure the line to the box in the the same way as Masraum's plug ( a strong connection), but then you could wire the internals of the box any way you please in a bullettproof box.
This may have been mentioned- I didn't read all the responses, but this it how I'd go about it.
Good luck.