I raise my trailer using a combination of bottle jack and garage roller jack, as needed. Once up high enough, I use jack stands. After all that, I grab a few chunks of 6x6 or 6x8 wood (pieces of "landscaping" or railroad ties) and put them under frame points. This is basic "cribbing". I may use the wood just as an emergency stop - quick job - or I may lower the trailer onto them - long job. The nice thing about the wood chunks is that they are big and square, so plenty of room for the trailer to sit on them and they won't move like a bottle jack will.
The last time I did all that was to get 4 new tires. I lifted and secured the trailer, took off the wheels, and brought them to the garage for new rubber. I saved a small amount (mounting charge), but more importantly I know that the garage did not overtighten the lugs nuts with their air wrenches (which seems to almost always happen to me). Most of the rest of the important stuff under my trailer can be reached from the sides.
