Soundguy has an excellent picture for good wheel chocks. Make sure the trailer can't move!
I would prefer to not use the stabilizer jacks for holding the weight of the trailer, even though I agree with dodgeguy. Try using wood blocks under the A-frame of the tongue if you don't have a tripod as Soundguy posted. As you lift the trailer, put blocks (4x4, 6x6, I have found 6x8 to work well because you can just flip them around for different heights) under the tongue's A frame, lower the trailer, retract the tongue jack, then add more blocks under the tongue jack to then lift the trailer higher.
After you figure out your best way to raise the trailer, then cut custom pieces of wood to fit as you are raising the trailer so you aren't balancing different pieces of wood each time. Label the wood, and don't use them for anything else so they are always available when you need them.
After saying all this, it might be better to just buy an adjustable tripod that fits under the hitch.
Or you can do something entirely different, lol. Just be safe!