Older frames are
light gauge metal and the newer ones are thicker.
When I fixed mine I replaced the frame from where the frame is doubled to the front hitch.
Here is what I did in front of the door to make it stronger.
I brought the frame to the very edge of the body and eliminated the bends as this weakens the frame and it also damages the tubing with the inside bent in and the top and bottom bowed.
This is what came out of my 1985 16'
Scamp.
In my trailer I modified the front for a front wet bath and a part of that was adding a pair of rectangular tubes as a crossmember from one side to the other and you can see that in the first picture.
The frame is doubled in the area where the floor drops 6" and then the top (I think) continues forward to the bend and then the hitch. I doubled that and then tapered the bottom one to spread the stress over a greater distance.
I fabricated a new vee to a new hitch that has the normal 55* angle and fitted the new vee to the new frame that I brought forward and welded the angle added the cross member there and added fish plate gussets along the outside.
Good luck.