I do mine on the bench, with the fork tubes out of the clamps.
1. You have to remove the fork seal holders. I bought the tool (which is a "pin wrench" where two pins fit into two holes and you just screw it off). You CAN fight the thing off with a strap wrench and a lot of leverage, but if it's on there tight with years' worth of internal corrosion on the threads, it'll be an epic battle and you MIGHT squash the chrome holders or scar the finish. I like the tool.
2. You have to pry the old fork seals out. This is pretty straightforward but they can be tight - don't damage the interior surface of the slider.
3. You have to drive the new fork seals in. BSA makes a special tool for this that centers the seal driver and makes sure it goes in square. After trying to tap one in with a punch by going around the diameter and trying not to cock it in the slider (and then damaging the seal when the punch slipped) I made a driver of my own out of a pipe nipple of the right size and a little handwork with a file. Drove right in then.
4. You need a tool to pull the forks back into the clamps when you're done. The manual
says that if you don't have a special tool for this, you can screw a broomstick into the fork threads and use that to pull it up into the taper. All that's ever done for me is to leave a bunch of broomstick shavings inside the fork. I bought the tool and quit worrying about it.