I'd extend the stabilizer jacks out at least a smidge over halfway. They're too short to be doing their job. I'd also take them off the concrete blocks and set them onto some wood, for cushioning.
Also, the one big block of wood for both tires isn't helping, imo. It's helping make the trailer move as one unit! The more points of contact to separate pieces of wood, the more stable.
I'd also look at one of the BAL (brand) X-Chocks
(THE EXTENDED VERSION FOR SPREAD AXLES) for at least one set of tires if not both (approx $90.00 for a set of 2)
Extended version looks like this:
Hope this helps!
WoodGlue