95% of the people will not like my frame since I am not added any fish plate. A full penetration weld is just that, the weld bead is the full thickness of the material. This is done by beveling the rails and leaving a small gap before welding. Once welded, you will have a raised bead on both sides of the rail.
I then ground down the weld so it could be tested. A machine like an ultrasound and jelly is used to look for and air gaps or disturbances in the metal. Also, grinding the weld smooth avoids any stress spots or sharp edges.
If the weld was not 100%, I would add a brake formed channel to fit inside the rail. This is much better than a fish plate or boxing plate.
Now, off to the bed. I completely disassembled the bed and cut down the floor pan. 12" off the front and 7.5" off the rear.
I drilled new front and rear mounting holes in the pan and bolted it to the frame.
You can see it still looks factory.
For the rear, I saved the rear cross sill and put it back on the frame and under the pan.
Then I started to tip over the 1/2" of floor pan I saved when I cut 7.5" off.
Once fully tipped, I plug welded the pan back down to the cross sill. The floor is now a SWB pan and no splicing like all others I have seen here. I saved over 10' of weld and kept my original paint.
Now off to the bed sides....