I recently assisted in reassembly of a '52 3100 bed. Another gent I worked with had a short socket that he welded a small stepped ring on that was used to capture the washers and nut like the plastic tubing idea. Even with his modified socket, we probably dropped or knocked off the washers more times than not - argh!
As Charley mentioned there is a need for a deep well socket which makes that type of modification difficult to use as the nut falls all the way to the bottom of the long socket.
Just thinking out loud here, but wondering if we could take the foam/rubber sleeve from an old spark plug socket (or something similar) and trim the outer sides down to fit into the 7/16" deep well, leaving it long enough to support the nut close to the end of the socket while still letting the sleeve keep/hold the washers during the beginning assembly???
Once the washers and nuts are started, it's easy to go back and tighten them with a second socket that doesn't have the modification (or simply remove the inner and outer sleeves and use the same socket).
Thoughts/suggestions???

Dan