Yes the braces do help quite a bit, but mostly on the front of the trailer where you have some weight and the strength of the tongue A frame. On the rear of a light weight trailer they help but I think a X brace style connecting the two would be better.
I am using the Lock Arm stabilizer bars from BAL
BAL - Innovative Products for the RV Industry
I would of made my own as well but the material I had on hand cost twice as much and I was pressed for time.
I also second a good set of locking style wheel chocks like the ones from BAL or similar. I was really suprised the first time I installed them before even putting down any stabilzer I could tell the difference.
You also need to look at the crossmembers if you have the C style jacks. If there is any flex or space between the jack and crossmember it will allow more motion in the trailer. I replaced the both the front and rear crossmembers on mine. Again biggest improvement in the front.
Have someone push on the trailer while you watch them you will see where the flex is. With a lightweight trailer you will never get rid of it all because there is not enough weight and the frame will start flexing.