My opinion, it is best to keep the suspension as level as possible. In some cases that means blocks under all the low side tires. Other times with a front to back slope, some of the tires will not need blocks. And finally, most of my blocks are 1-1/2 inches thick, so if that is too much, then again some of the tires will not be on blocks. So, do what you need to do to get the trailer level AND balancing the weight evenly as possible across all the axles/springs.
Texas Baptist Men-Retiree Builders member since '01
13 Silverado 3500HD D/A, 2wd CCSB srw, custom RKI bed
11 Cruiser CF32MK