[horsa]

Railroad Ties / Sleepers are what I use but they are just like the cribbing blocks when cut to shorter lengths to keep things manageable. One tie can be cut into four shorter blocks and they are pretty solid for holding the weight once you jack the vehicle up.

I've always used a 3-ton floor jack to get one end of the vehicle up and then move the blocks into place so the jack isn't under load later when working underneath the carrier. Used to place 5-ton jack stands beneath the carrier before the blocks but I had one literally fold up and collapse. Likely from my having been in the vehicle earlier and doing work which possibly caused the load to shift. It didn't fail while I was in or under the vehicle fortunately.

Blocks are certainly safer, even though they are harder to manage than stands. Getting crushed will ruin the rest of your day. Assuming there is someone handy that can jack the vehicle off whatever part of your body is pinned.