Ok, seeing as I posted the picture I guess it’s only fair that I answer some of your questions.
All extrusion in the picture, excluding the bearing blocks, are item profile 5 20x20. The bearing blocks are item profile 5 20x80.
The only t-nuts used are to hold the ‘belly pan’ to the bottom of the chassis. All the rest are what are called standard fasteners (see picture).
For the bearing blocks we tapped the ends of the extrusion and milled clearance holes for M5 screws that go through the 20x20. This eliminates the problem that we see many teams facing each year with their pillow blocks shifting around on them. This also allows us to easily remove the bearing blocks if repairs are needed by simply taking out the four screws that hold them in place.
We weighed everything you see in the picture above at just over 20 pounds.