Hi Bob!
I believe you've got the right idea about what to do... The only questions I have for you is:
1) What do the contract requirements call for with respect to the Base/Filler Metal, welding process, etc.?
2)Does the USN/Contract requirements want this trolley assembly to conform to AWS D1.6 or, are they requiring you to follow NAVSEA/NAVSHIPS specifications??? I would definitely seek to clarify this before you start so it does'nt come back to bite you in the you know where - Capish???
On a personal note: I never heard of the USN use AWS codes. My experience has always been their exclusivity of using NAVSEA/NAVSHIP Specifications but then again, things inevitably change although in the USN's case, I highly doubt it! Who knows, I've been wrong before but, unless they already have women on Submarines, no offense to the females but until then, Submarines will be built according to the specifications championed by the Late, Great Admiral Hyman Rickover, and the rules of maintaining them will more than likely remain the same also. Still, I could be wrong on this since it's been awhile. ;)
The only exception to the rule would be to build something that will not become part of the Submarine itself, and that's what this trolley assembly is categorized as such so, then one could specify AWS D1.6 in this case. Hmmm, I guess I already answered question #2. ;)
I would also agree with Chuck's suggestion of using 310 ss filler because that is what we used to use on almost anything stainless external of the pressure hull, and in some locations/applications thoughout many of the SSN's (Sub Ship Nuclear - usually Attack submarines) and FBM's (Fleet Ballistic Missile submarines otherwise affectionately named "Boomer's" or designated SSBN's = Sub Ship Ballistic Nuclear) I worked on while serving in the USN and afterwards while employed at General Dynamics Electric Boat Shipyard Facility in "Rotten" Groton, CT.
They'll probably require the same but then again. the only way to know for sure is to clarify it with the USN folks, or else they'll turn around and bite you in the you know where for not doing so in the first place! :)
Finally, the way they (USN) Degauss these babies is pretty "NEATO" to say the least so, I do'nt think there is going to be too much of concern unless there is enough potential for the trolley assembly to transfer any leftover residual magnetism back to the Submarine hull once the degaussing is completed which is probably your own concern, and would be appropriate in this case.
Respectfully,
Henry