One factor in anything but a large trailer is that they do not have regenerative braking, so whatever margin of the braking is done by the trailer is all lost to heat. So the 2-digit estimate for range with a decent-sized trailer is probably good for all but perfectly flat non-stop driving.
“One factor in anything but a large trailer is that they do not have regenerative braking...”
Sorry, need to PROOF-READ:
What I MEANT to say is the following (quite different):
“Trailers, as far as I know, DO NOT have regenerative braking, as electric vehicles do have. Without regen, all breaking energy is lost to heat, thereby killing range.”