Old-Biscuit wrote:

If this block would have been turned on it's end, instead of it's side, and a board placed on top and bottom, this would have never happened. If cinder blocks are so fragile, then we've got millions and millions of building around the world that are subject to crumbling, so we all better get out of wherever we're sitting right now, because most likely your house is sitting on a cinder block foundation, if not on a concrete slab.
If salt deteriorates cinder block, then the building industry is also in serious trouble. How many embankments along the highways are made of cinder blocks too? Hum? Salt is not the damaging factor in cinder blocks. It's the little pours and holes and dimples that hold water, freeze, and cause cracking that makes them crumble.
The strength of the cinder block is when it's turned on end, not it's side. And it can have no movement, has to be on something solid, to be solid. On dirt or grass, there's to much give without a proper foundation UNDER the block.
What I'm saying is, if used correct and for the right reason, cinder block are very strong and will last a multitude of events, including salt. But, as this photo clearly shows, this is absolutely the wrong way to use one, especially for a camper.
About the bottle neck jacks: They are very strong too. I have a set of them, and the are capable of supporting my entire camper (with wheels off the ground). By themselves, they are very strong and restrict trailer movement to some degree, better than than the factory installed scissor jacks.
These jacks have been around for a long, long time. My parents used them on their 1963 Phoenix travel trailer in 1963, as back then, jacks did not come factory installed. When I got my own pop-up camper, some 30 (plus) years later, one of the first things I got was a set of these exact same type of jacks, and have been using them ever since in addition to the factory installed jacks. But I don't put them under the existing jacks. I end up having 8 jacks supporting (4 factory installed and 4 bottle jacks). (Makes for great support for winter storage, but too much work when actively camping.
Placing the bottle jack under a scissor jack would provide stability for the camper, only as strong as the collapsed position scissor jack will allow (this doesn't make sense to me).