The fiberglass trailer frames are based mostly on the original Boler
design with the underslung floor with a dropped section of frame at he door for a flat floor for easy access.
Under the door is a section of the same tubing as the main frame is made of.
This section is laid with the long side horizontal instead of vertical making it weaker than the vertically oriented sections.
The door area is weaker in the vertical plane where the loads actually are and this causes the stress to flex in this area, particularly at the places where it reconnects to the vertical sections of the frame.
The frame flexes here and also this causes stress to be reflected on the opposite side in the bend where these trailers also have breaking problems.
I reinforced this area on my frame rebuild along with replacing the flat sheetmetal carry through from the left to the right.
Here is a picture of the reinforced part of my frame.
Here is a picture from the other side showing the added reinforcement.
If you noticed the frame was also lengthened to bring the "bend" forward to allow for the installation of a front bath.
I also added a cross brace between the two bends to carry and share stress from left to right.
Fron the front outside of the trailer.
I also added reinforcement from the cut off section of the frame that the axle
sits on all the way to under the section that goes forward to form the tongue.
The two 1 1/2" X 3" sections are welded together to make the 6" deep frame section.
I used heavy wall tubing instead of the lighter gauges used when my trailer was built.
I also added 1 1/2" square tubing to the periphery of the trailer to bons the floor to and also added steel wheel wells at the same time for clearance for larger wheels and tires
These added braces hold the floor and then that floor is fiberglassed into the shell making it shell a part of the stiffness of the overall trailer.
All of these and other reinforcements and additions has definitely added to the weight
of my trailer, but I am also pretty sure that it will out last me as well.