Need information about 2012 Kia Sedona LX towing a uhaul 4x8 trailer. Do I need the cooling kits? Also, will I have any issues with transmission latter?

I think the best idea is to pull the Kia with a u-haul truck or van just get one with enough room to carry all your hauling and has a hitch too, for your rented tow dolly for the Kia. Most 4x8 trailers do not have or need trailer brakes. If you are pulling the trailer an extra trans cooler that is run parallel and uses your radiator first then goes to the new extra cooler before going back to the trans is best way to go. You can always add a oil cooler for your engine it will help like the trans cooler to extend the life of your ride. I would think that anything you could put in a 4x8 enclosed trailer the kia would pull. Keep the heavier items over the wheels and not up front as it will transfer the weight to the tongue and then on to you Sedona rear end causing handling issues. But like I said if your concerned about the wear and tear and may need some extra room too, rent the truck and tow dolly.

Thanks enginecreator, These oil and trans coolers? What exactly are they? All the reviews and question/answer sites seem to mention these nonchalantly as if you're just plugging in a fuse. It seems like a time consuming and expensive add on. Could you shed some light on that for me?

Not really, The trans cooler mounts to the radiator with pull tabs is the easiest. The trans line runs to the radiator in a separate area not mixing with coolant. After going threw the radiator the fluid is returned to the trans by the return line. It is this return line exit from the radiator that is routed to the new trans cooler and back to the return line. The oil filter mount can use an adaptor plate that the oil filter still mounts to it or the oil filter can be remote mounted too depending on which adapter plate is purchased, this plate has port holes that run engine oil threw it out to the in line on the oil cooler and out back to the 2nd return port on the adapter plate. Some engines already have a oil cooler and you do not need one or can upgrade.