There have been quite a few owners that have understood the problem, and made modifications to protect dump valves during the refurbishment and repair of their Airstreams.
Thor, as the current manufacturer of the Airstream product line, not so much, frankly.
Some older models placed their dump valves and sewer connections in the rear bumper.
Many SOBs have the entire drainage and dump system running for multiple FEET along the side of the trailer, hanging out there vulnerable to a road debris strike, and have no protection whatsoever. I guess it's the "industry standard" to make it easy for a fast dump underway like you experienced.
And yup, the last tire failure on our Airstream ripped out the wheel well, water pump, and a bunch of plumbing inside the AS, but managed to miss the dump valves somehow. When I add lift blocks to the axles, I also plan to add a skid shield to the dump valve area--then I'll have clearance to do it...
Currently, the vulnerable bits are out there in harm's way...
Rich, KE4GNK/AE, Overkill Engineering Dept.
'The Silver HamShack' ('07 International 22FB CCD 75th Anniversary)
Multiple Yaesu Ham Radios inside and many antennae sprouting from roof, ProPride hitch, Prodigy P2 controller.
2012 shortbed CrewMax 4x4 Toyota Tacoma TV with more antennae on it.