this is an old 1940's(?) one tonne truck that my sisters and I played in as kids. My mom and I fixed it up for the kids to play in.
Step 1: Mom and I took the tailgate off and cleaned it out
Step 2 and 3: Mom and I built the stairs and then we built the braces and the joists. Dad helped by grinding off some big metal screws that were in the way.
Step 4: Mom and Dad altered an old canvas and attached it to the top.