I think regen braking only helps if the load is on the bed. If it's on a trailer, the trailer will have normal breaks and a lot is lost. (Edit: spelling)

It also doesn't help if you have a long freeway trip where you don't brake.

Trailers may not have regenerative braking today, but that's a chicken-and-egg problem; trailers already have wiring hookups, and once EVs become the default for personal vehicles, it's easy to imagine that regenerative braking will become standard.

braking