I always jack at where suspension mounts to axle, or where the suspension mounts to the axle. I assume those points are designed to carry the weight.
Tire change; You carry something to build a ramp to level the camper for use right? And also while the jack is moving trailer up/down is when it most likely to slip, drop trailer, right? And most jacks, to operate you must be in, or close to where the trailer will fall if it does. And if the wheel and tire is mounted when it trailer drops, trailer, and more important, you are less likely to get hurt.
Given all that, IMHO, the best plan is to pull the flat up on leveling blocks to get center of axle as high as it sets when the tire is inflated. Break nuts loose, then jack it off the block. This means, 1)Don't need to jack as far, so less chance to slip. 2)and most important, when you move the ramp you have room to get the inflated tire in place, never need to "Up a little more" with no wheel in place.