What has worked for me on a steel bodied National Duolian, is the ( out of production, of course ) Barcus Berry Dobro pickup.
Since it is magnetic, it also reacts to the steel body shaking, ultimately giving a great " National" sound, but without the screechy hassles.
I learned about this pickup from two Great Players, who are unfortunately no longer with us, John Campbell and Chris Whitley.
What I like about this setup is that you can walk up to a Fender Super Reverb, and JUST PLUG IN . No Hassles, no soundman , no worries, mate !
For actual gigging use, it's a hard setup to beat.
Additionally, no holes are cut into the guitar, the pickup is thin and surface mounts.
For Recording, I use the pickup to a remote amp, and good microphones on the National.
Here is a link to a moody "When the Levee Breaks" on
http://www.myspace.com/DruLore ( AUDIO ONLY ) It is one take, one of the strings was tuned down an octave for the Drum/ Drone effect. The file is to large to fit here, just click on "Levee " in the upper right corner of the page