An LE van might not be the best choice for you given your situation. XLE comes with a motorized hatch, IIRC.
Straps can be problematic if they don't retract, as if it's mounted on the inside it will invariably end up pinched in the seal on closure. I have heard of aftermarket kits, but the Sienna system is a bit unique (different from the RAV4 and Highlander in architecture), so likely not as common. Perhaps the inner panel, motor and drive from a wrecking yard Sienna could be grafted in.
Straps can be problematic if they don't retract, as if it's mounted on the inside it will invariably end up pinched in the seal on closure. I have heard of aftermarket kits, but the Sienna system is a bit unique (different from the RAV4 and Highlander in architecture), so likely not as common. Perhaps the inner panel, motor and drive from a wrecking yard Sienna could be grafted in.