Stretched

L brackets bolted to the side of frame that go to the bottom of top frame rail. Lay your plate on top of them drill the holes all the way through. Using a chop saw cut the bolt heads off and plug weld them in the plate. Use patience and a tiger paw wheel on a 4” grinder to smooth out the weld. When your done you’ll never see the welds and you have a smooth clean top.

 

The first one we did followed an old Peterbilt manual I believe. Top to bottom of the rail cut at a 45. Top and bottom flange continued on at a 30 degree angle. Frame behind cab was set on blocks and the cut off was aligned to it. When a weld cools it pulls and you can find yourself out of wack real quick.
Later we just cut them straight in the center of a cross member or added a cross member there. Sleeves in some cases. As you get longer more cross members per foot should be used to my understanding.
I like wore outs idea of L brackets.

 

Those were just for the deck plate between the rails. I may have misunderstood I thought that’s what he was asking was the deck plate.

if stretching see above that’s how we done it