We use wheel chocks and the "lego" style blocks for 2 reasons. 1 - to give the small jack pads something firm to sit on and spread the load and 2 - so the jacks aren't extended all they way (when on an un-level site). The more you have the jacks "vertical" the less stable I've noticed the rig becomes. Think of a camera tripod. With the 3 legs spread out it's very stable. If you take the same tripod and don't extend the legs, it's very unstable.
I've seen people (aka, my brother) use scrap pieces of 2x6, or larger, for the tongue and corner jacks. However, there's always a cup (or warp) to the boards so the boards rock like crazy and no matter how much I tell him he doesn't seem to get it.
2013 GMC Sierra 2500DH CC, 4x4, D/A
2016 Forest River Vengeance 25V TT/TH