Dutchmensport - Jack stand I was talking about, was not a hydraulic bottle jack. It was this:

It is not very strong.
OTH, hydraulic bottle jacks are very strong and are the only tool that should be used for lifting a trailer for servicing wheels etc. I've been told not to leave a hydraulic jack in extended position for long time, or the shaft will corrode.
This jack stand on the photo will corrode too, if not lubricated often. Some stands of this type are aluminum, but only the frame, while the screw is steel.
Cement blocks (or fake cement, whatever) can't always be placed on the end, there might not be enough room. But they sure need a solid, flat and wide support both below and above.