That's a good one, I will try to make one of those shocks like you described... I didnt buy them because they are expensive... $7 looks a good price
Yesterday I added the two BAL Lock-Arm Stabilizers on the jacks on the back of the trailer. One on the street side and one on the curb side.
When I unlock one of them I can shake the trailer easily by hand, after lock both of them the trailer is much more solid and does not shake that much.
I will be camping during the weekend, lets see how that goes, right now looks very promissing.