I knew a guy who could reverse up a driveway with a trailer only using his mirrors & at the same speed as if there was no trailer at all
I am no where near that good, but I find the longer the trailer the better.
I once had to reverse back down a steep gravel road (well actually we were more like dragged back down) with a car trailer loaded up with a mates Mini which had been through a flood & had a big layer of mud inside the floor, so it was quite heavey - after we could not get up the hill due to too much loss of traction (and too much clutch slipping under load)
, I did not have much choice over the reversing action as my brakes could not hold it on the hill & we were dragged to the bottom of the incline with me just trying to steer it
(ended up getting a mates dad to tow the trailer out with his 4wd
We have a 8x6 box trailer that we use for camping & I was starting to get the hang of reversing that with my work car (Holden Astra hatchback), which was quite small & I could see quite well out the back window, but I now have a new company car without a tow-bar, so the next time we take the trailer I will need to take my fiancees Magna, which has bad visibility when reversing, so I will have to retrain myself