I believe a "WOOHOO" is in order.
I spend my working day in an engine room in earmuffs, which gives me thinking time. I was looking forward to getting off and home to try out AndrzejL's Night Commander suggestion. But the whole day, I kept coming back to his note on his homepage: be sure SSH is started. I checked. It wasn't, on either machine. Setting it on boot was all it took to make GSSHFS light up, and around a peculiar request for administrative privilege and opening into root's folder without allowing me to do anything as mdm, it just works. I close out of root and reopen PCManFM as me, and my mount is there and accessible.
I also started network-auth after reading briefly in Goooogle of its part in sharing passwords. Feel free to tell me not to be silly if I shouldn't have.
I'll let the dust settle, watch Andy's set-up video for NC, and then mark this <SOLVED> for my purposes anyway.
Thank you for all your help in this.