Thank you all so much for your responses! We'll look into a winch-type option & see if that will work.
Yes, the reason we can't back it in is because the trailer is perfectly vertical in the back, and with the driveway slope + our low eaves, we would need to stop well away from the house, leaving the tongue hanging over the sidewalk - a no-no in our town. Even a teardrop such as an R-Pod is too tall for our eaves.
Conversely, if we pull in (forward) with our truck, it would box the truck into the garage with no way out.
In addition, the trailer will be parked on that slope (not just moved through it), which brings another set of problems.
*Sigh* We may just have to resign ourselves to paying storage if we get this (or any) trailer!