Why not jack trailer under the spring plates?

I have seen a few cases, of people actually putting their floor jack in an obvious wrong part of the axle tube. One case, two floor jacks, one under each axle of a fifth wheel, landing legs down, and the jacks placed between wheels and axle centers. He was packing bearings, too late anyway, so I didn't comment on his placement of jacks, lifting the whole side, with landing legs down.

There is quite a number of adapters for bottle jacks, that will cradle the axle tube, in the U-bolt area. I just made a wooden block, pictured in the recent travel trailer section, asking similar question. Works good for me!

Jerry