Mine uses all square head screws. I think they're called robertson head screws. My subfloor runs under the 2X2 wall studs Attaching to chassis ears every so often. What is racking and what does it look like? I'm also replacing all the fiberglass junk with spray foam closed cell insulation. I plan on leaving the aluminum siding on until all the interior luan is replaced and subfloor. Although, The siding is NOT stapled to the floor. It actually hangs below the undercarriage by about an inch or so.
As far as building like a site built house, I will use 2X2 studs still and light material. I don't mind using "rv type" material as long as its a more universal kind and doesn't have the look. Like a plastic sink.....Stainless weighs the same and looks so much better. I'm doing alot of balancing with weight vs. cost, functionality, and appearance. Also carefully planning out the floor plan. Thinking of keeping the same plan but making minor changes. mine doesn't have the bathroom closet but instead a sink and the "closet" is over the elec. distribution block. Thinking of deleting the bathroom sink altogether and enlarging the bathroom area or putting a closet there. Things like that. Trying to not only keep weigh down but also evenly distributed.