This is the gallon bag companion to the quart bag holder shown here. http://www.thingiverse.com/thing:1291420

If your print bed is large enough, use the "gallon foot", "gallon leg" and "gallon top" files.

However, the top of this one is near 7 inches long, and wouldn't fit on my 5.5 x 5.5 inch Afinia build plate. I had to piece it together.
2 "Top Half" and 2 "Top Boss" files were required to be printed and assembled.
(With some careful positioning, 2 feet and 2 legs will fit on the small bed.)

I friction-welded the top halves and boss-pieces together.
http://www.thingiverse.com/thing:1807093

One photo shows a weld detail.
The welded construction is strong. The photo shows it supporting a gallon of water. Near 4 kilos, 8 pounds. The feet splayed outward a little bit from the side-pressure, but there is some flexibility and I will never be putting that much in a bag, so I'm not concerned about it.

Glue or adhesive should be plenty strong enough, but my intention was to weld it and the joint on the top halves was designed with that in mind. I suggest welding it.

As with the quart bag holder, you will probably have to file down the corners, at both ends of the legs, so the parts easily assemble and disassemble. A tight fit will break something. Make it smooth, but not sloppy.

Seems like there's lots of files, but half are the Metric versions.