Pulling the plenum / IH Some pics !!

[WVZR-1]

That box will do well for the 'first' of the double box. If you wrapped it well in that box and then used 3/4" or 1" Styrofoam sheet on all six sides of it inside of another box you would be probably fine. I'd center it lengthwise in that box and fill the ends, paper is a great packaging product. For the second box if you've a smaller LCD flat panel of a recent purchase or check some local stores they're quite substantial. 1" Styrofoam is the preferred here I'd say.

An auto dealership generally has some really good packaging hanging around in either the parts dept. or the body shop. If you've some relationships at one or a few I'd use them.

I'd consider two boxes total for the ship. For the IH's I'd find a box suitable for each one and box them and then package them in a single larger box that is as well packaged as the plenum will be.

If you could find an appropriate box then the three singles inside of a single if well packed would do likely as well like Clint mentioned.