Mark....my landscape trailer for many years was the same size as yours, except mine had sides - tall enough to hold materials, specifically mulch.
With these sides......I could get 4 cubic yards easily each trip.
Wooden floor like yours and I used a plastic scoop shovel to handle the material.
I had the conventional scoop shovel with the D handle - and also long handled ones - which allowed me to reach further in.
Piece of shade cloth to fold over the top if traveling ant long distances but most of my work wasn't too far so typically I didn't need it.
I used this trailer over the span of 20 years. Had parts of it repaired over the years too including the tailgate/ramp, metal fabric, axle springs, lights, and jack. It sat outside on the barrier island so over time the salt air took it's toll. That said it paid for itself over and over every freaking year!
I carried bulk materials, plants, trees, irrigation materials, equipment, you name it. Even used it for motorcycle transport!
This is a photo of it after one of it's repairs having some metal fabric replaced. You get the idea of it's design.
My tailgate/ramp was easily removable too which really helped.
I like your idea of using the totes but wonder if your trailer just had taller sides it would be simpler and easier solution (?) Even if you made them "removable".
