I wasnt going to reply anymore as its pretty clear there is nothing on this forum that you either dont already know or dont want to hear but since the safety of other road users comes into it i figured i better post these pictures....
They both show the computer simulation of the loading on each side of the trailer based on forces being applied at the points you have indicated. Picture 2 follows from the bottom of picture 1.
As you can see, the first shows a simple forces diagram showing the current set-up of your trailer....
I have allowed for a 6" landing area where the axle meets the side rails.
I have also set this up on the assumption that you have used a 50B grade steel or similar.
I have simulated a 200kg force forward and a 210kg force aft (at the points that the swingbeams connect to the rails.
This gives you a total loading of (200x2)+(210x2)= 820kgs
If you loook at the second picture you can see that in your case you are on the absolute limit of the permissible stress allowed in the steel. (Highlighted red, 208Mpa out of 207Mpa m, ax). Beyond this you risk deforming the steel leading to possible failure. Incidentally It also shows a maximum deflection of 18mm
Keep in mind that i havnt subjected the loadings to any safety factor either.
Your best option to render this safer is to move the rear swingbeam further forward thus reducing the bending moment on the side rails.
But of course... you already knew all this didnt you?