The level of the chassis is a function of the height of the ball on the tow vehicle and the trailer axles. I would first look under the trailer and check the conditions of the axles. While the trailer is not hooked up and sitting parallel to the ground, not level to the world. Looking from the other side of the trailer at the arm that goes from the axle tube back to the wheel spindle. That arm should drop downward, on good axles, as it goes from the axe tube to the spindle. If it is pointing upwards the axles are shot. If the arm is parallel to the frame they are on the way out.
Now having said that you can still tow the trailer 4 or 500 miles as long as you lower the hitch on you truck so the trailer is riding parallel to the ground. If you leave the rig as shown in the picture, tongue high, you will be putting more weight on the rear axle that may already be at the stops.
Towing on older axles for that length of distance will not be a killer.
WBCCI 12156 AIR 3144 WACHUNG TAC NJ6
2004 Excursion 4x4
1991 34 ft. Excella +220,000 miles, new laminated flooring, new upholstery, new 3200 lbs axles