Literally one the most universally competent places to jack up about any solid axle is under the spring perches or u bolts.
There is nothing special about any of the probably 100 different trailers that I’ve tossed a jack under for one reason or another, that I’ve seen.
In general, if you support it there or under the frame (within reason) and something gets damaged, it wasn’t going to last anyway.
As always common sense applies. If you have a 3000lb buggy sitting over the axles of a toyhauler and you jack up the back corner of the frame, or something like that, you may tweak something.