So, something like this:



Note that my Gimp skills are severely ... gimped.

Edit: Whoops, forgot the backrest... but you get the picture.

I've done a mine and a B-i-L's using old MC package racks in-place of the pillion. Started with a Honda CT90/110 rack which is a nice size but hard to work with as the mounts are all bent thick sheet metal specific to the Honda CT series. Later I used a $5.00 one from a MC salvage yard on mine. For B-i-L's used a slightly smaller one that workded well. I cut off the solid square steel sissy bar and use a piece of bar stock across it for the rear support and then either weld or bolt the rear mount of the rack to it and have done 2 different ways for the front support. Mine is cantilivered to the OE front pillion pad spots and uses the same rubbers for support.  B-i-L's is bolted to the 2 front fender rail spots as I didn't see that possibility when I did mine. The supports were part of the Hard Bag installation pieces from the set I bought. Had no idea the spacing and size was exact for the Savage. I use a GIVI trunk and it is of better quality that the Chinese knock off JCW sells, but they both get the job done and the quick detack plate is nice if you want to use the flat spot to bungie something else on. Also I find the backrest (mine stays with the luggage rack so I can us it w/o the trunk) really minimizes the back and arm tiring when moving at road speed making the trip all that much more enjoyable. i think the s-40's w/o the sissy bar would even easier to fabricate, could even use hose clamps to attach to the cross piece and not have to weld to drill and tap like I did. Max

Could always remove the padding from the pillion seat and sew a zipper in the cover.  Then you'd have a "fender bag".  

Just a thought

I've carried a medium cooler strapped on the passenger seat, works great and acts like a backrest. I would like to find a medium sized carrier to mount on the back but I have a one piece seat.

Or use something like <b>this</b>...