The
Casita 17's are "tongue heavy", so 400 lbs is a realistic guesstimate. Your tow vehicle may or may not sag substantially; I'm not familiar with the Sorento's characteristics.
The height of the coupler will also vary based on whether your trailer has a lift kit which serves to lift the body above the
axle. The Dexter lift kit is comprised of two pieces of steel which are bolted between the
axle and the frame. It raises your trailer by 2-5/8".
https://www.etrailer.com/Accessories...71-707-01.html
Because the trailer is a 2006, there's also a strong possibility that unless the
axle has already been replaced, the rubber in the axle has hardened and the axle "sags" a bit. Replacing the axle is appropriate at something like 15 years and probably necessary by the 20 year mark.
For all these reasons, it would be best to level the trailer and measure what you have, and also to evaluate the condition of the torsion suspension in the axle.