Pulling the slides in isn't necessary.
Raise the rear stabilizers a few inches off the ground.
Place jack under axle at the U bolts if a tube axle. The U bolt is the brightly colored bit that looks like a big U.
If it's a torsion setup, place the jack under the frame near the tire. In the photo, see the piece of metal the hoses are tied to? That, just under the frame rail is where you put the jack.
Take wood under the trailer with you, once the tire clears enough to slip the wood under the tire, slip it under and let the tire down. Repeat for the other tire on the same side.
Check the level, add another as necessary.
Now, there's nothing to be worried about. Since you're not removing the tires even if the jack slips the trailer isn't going to fall on you. Don't be careless, but there's not much to worry about either.
Finally, put your stabilizers down and you're set.
If you don't want to, it shouldn't be hard to find someone that can do it for you.