Moosie, I do not debone any of my elk. I skin, cut off the quarters, and cut off the lower legs. I place the quarters in saddle panniers. I put the loins on top of the quarters. Ontop of that I place all my extra crap and tie my coat on the back. The head and/or antlers get tied on last on top where you would normally sit. One horse, one elk, and lead the horse out.
Are you using the canvas roll-up panniers, that go over your riding saddle? And then you stuff a front and a hind quarter on each side? And when you say loins, are you meaning the Backstraps, or the Tenderloins?
Are you putting a rack and a cape on, too (no, not on the Spike, but if you get a big bull)?