Disable and enable air bag system

you should be fine with the standard genuine Isuzu tow bar. The rear of the vehicle may be down a bit when fully loaded depending on weight of pop top. weight distribution in pop top is the key. You can fit heavy duty shockers (GAS) & air bags to rear suspension if needed for light vans. They go inside the rear spring coils. The Hayman Reece & sway bars will raise the rear & take weight off of the tow ball but this has not been tested by Isuzu & warranted. Sway bar hitch does not fit on the genuine Isuzu tow bar also. The best thing would be to talk to an Isuzu Dealer such as North East Isuzu Ute at Burton, Adelaide, South Australia to work out your best needs.

https://www.uhaul.com/Frequentlyaskedquestions/202/Trailertowing-Rentals

How do I find my hitch system rating? Your hitch system is comprised of three components, the Hitch that is attached to the frame of your car, the Ball Mount (drawbar) and the Hitch Ball. Each component has a rating for capacity. The LOWEST rating of the three components determines the overall rating of your complete hitch system. For instance, you can have a 3500 lb hitch and ball mount, with a 2000 lb ball. Your hitch system is limited to the 2000 lbs towing capacity. https://www.uhaul.com/Articles/Tips/33/How-To-Determine-Your-Hitch-System-Rating

if you want to fit the tow bar your self you should be aware that by fitting a tow bar it is a modification to the vehicle and requires a certified plate attached to the vehicle to cover insurance requirements and road worthy inspections
next most purpose built tow bars sold by auto shops will pick up existing holes in the sub frame mand you can get a harness that piggy backs onto lights on one side for the trailer
Best talk with a tow bar retailer/ fitter as they can certify the bar and the fitment and have a harness in stock

The sensors are sensing the tow bar, either remove it or disable the back up sensors.

the most important thing in towing is knowing the weights and limits of the tow package,, In your owners manual, it should list the towing capacities , if you have an after market tow hitch, check to be sure that the hitch is rated for the vehicle, Just because a tow hitch is placed on a vehicle, doesn't mean it can tow just anything, again,, the weights must be compatible for each vehicle. I had my vehicle equipt with a tow package that is added to the transmission of my vehicle to enable towing

{: ) The PARK ASSIST OFF message will be displayed when the parking assist system is disabled due to conditions that disable or inhibit the system. The object alarm module requests the DIC display PARK ASSIST OFF when it detects one of the following conditions:
• The parking assist system is manually disabled using the driver information center (DIC). • An object is attached to the rear of the vehicle, such as a trailer, bicycle rack, trailer hitch receiver, or tow bar. • The object alarm sensors are covered by snow, mud, dirt, slush, or ice. • The vehicle bumper is damaged. • Excessive paint thickness on a replacement object alarm sensor. • The object alarm sensors are disrupted by vibrations, like those caused by a large nearby vehicle or from heavy equipment such as a jackhammer.
The SERVICE PARK ASSIST message will be displayed when the object alarm module detects a malfunction in the parking assist system and the system is disabled. It could be one of your sensors is at fault or even the module.

Obtain a tow wire harness. Then tap into the existing wires on your vehicle, if it is not prewired for towing. If it is prewired, you will notice a bundle of wires near the rear of your vehicle. Attach these to your tow wire harness and then to your tow hitch.

• You can tow any front wheel drive manual transmission vehicle as far as you want and as long as you want. As an added precaution, you might want to consider a lube pump or axle lock to ensure that no transmission damage will occur.
• Most 4WD vehicles with a manual transmission, manual transfer case and manual lock out hubs can be towed on all four wheels safely with no problems.
• If your 4WD has no manual lockout hubs and/or no manual transfer case, then you will need a coupling device on the rear drive shaft to tow it safely
• Before moving the towed vehicle, check the following: transmission fluid level is full, release the parking brake, start the engine, shift the transmission from Park to Drive, shift from Drive to Neutral, turn off the engine, leave the key in the Accessory (I) position, make sure the radio and all accessories are turned off.
  
  The steering system can be damaged if the steering wheel is locked. Always leave the key in the Accessory (I) Position to prevent damage to the steering system when towing behind another vehicle.
  
  Some recommend starting the engine and shifting the automatic transmission (if so equipped) through the gears approximately every 500 miles and shifting from Drive to Neutral before shutting off the engine.
  
  Safe towing of a vehicle with four wheels on the ground behind a motorhome can only be done with a supplemental braking system including a break-away feature.
  
  SEVERE AUTOMATIC TRANSMISSION DAMAGE WILL OCCUR IF THE CAR IS SHIFTED FROM REVERSE TO NEUTRAL AND THEN TOWED WITH THE DRIVE WHEELS ON THE GROUND.
  
  You can avoid certain kinds of handling problems by making sure that your vehicle is towed with the tow bar as close to horizontal (parallel to the ground) as possible. This prevents your vehicle from "riding up" or "running under" the back of your coach during hard stops. It also avoids excessive stress on both the hitch receiver and your vehicle's mounting brackets.
  
  Most newer vehicles will not add miles to the odometer while they are being towed. Such vehicles have an electronic odometer which will work only if the key is in the "on" position. If your vehicle is an older model and does not have an electronic odometer, you will need to have a Speedometer Disconnect to keep miles from adding up on your towed vehicle.
  
  Never ever back up with a vehicle attached to your coach with a tow bar. Backing up is the most common way of damaging your tow bar or towed vehicle.
  

at a guess you need new valves or air bags for the suspension. not cheap & best left to professionals. whenever you have to jack or tow vehicle to a point where the vehicle is out of level, make sure to disable the air suspension using the switch located near the front seat passenger's feet up under dash, in a corner. this helps prevent damage to air bag system & repairs