I stopped by my local music store and chatted with the owner who had D-rings put on a case for a very expensive mandolin ($3000 Gibson with Bill Monroes autograph) -- they failed fairly quickly, leaving an ugly hole in the case!

So the word on metal attachments seems negative, especially given the weight of a D-28 and a resonator banjo.

Bill - I'd like to see your design. I was contemplating something like that, around the waist and the neck, although I have since found listings for Small Dog case covers at Janet Davis Music for just over $100. They seem to have the attaching straps on opposing sides of the case to make it balance.   

Mooh - Christine Laving of "Four Bitchin' Babes" fame recommends packing your clothes in a soft gig bag and your guitar in a hard-shell case, then swapping them when you get to the Festival, etc. for lightness. Of course you've got to be careful not to use the guitar polish for deodorant or the Gorilla Snot for hair gel! :)