Blocking up a 2h BP can be done. But It's more secure hooked up. Even the bigger GN trailers. You can load with out trailer hooked up. But I would think all the rocking that the trailer is doing isn't good for the jack itself. You have a chance of messing up the jack leg. My trailer had to be fixed due to the trailer moving back after it was unhooked and wheels not blocked. Was before I bought it. So when you do anything with a horse and trailer it's better to be safe than sorry....jmo
Never Ride Faster than your guardian angel can fly
"UNTIL ONE HAS LOVED AN ANIMAL, PART OF THEIR SOUL REMAINS UNAWAKENED"