Ridecamp: [RC] Slant Load Trailers

I'm hoping for some good advice here.  I have a brand new (well its one year old, bought it used) slant load trailer.  I've previously only had straight load trailers that worked beautifully.  A few lessons and even the youngsters get in with the rope thrown over their backs.  I DO NOT have to get in there with them, I feel very safe.  Now I have this slant load that 3 out of 4 horses find is ok.  The 4th horse, however, thinks the slant load is clearly the home of some horse eating monster (or maybe the Devil) and he will only stay inside if if I stay inside it with him (aaargh!).  Its going to be really hard to drive the truck and ride in the trailer with him!

I'd love to hear some good tricks (no offense, but can we skip the Parelli, Lyons, Roberts, video etal stuff?  I've pretty much tried that) on how to practically make this work.  As I said the other 3 have adapted fine from a straight to a slant load.  The 4th guy has other ideas.

Anybody else with this experience?

Sylvia & Chance (IT IS the home of the Devil, I just know it!)