Dittos to everything said above. If you have to raise the bed, by all means brace the hell out of it before you go under there!!
The reason for leaving the plug out the first time you let it down is,in case you overfill it. If the plug is in, you'll blow out the seals when you let it down.
If it's at all possible to work from below, without raising the bed, that's a better option, at least from a safety standpoint.
On mine, I just went to the farm store and got their basic hydraulic fluid.
