So, I’m hearing that for towing, (8500# travel trailer. Yes, the first thing I did was add a set of Timberline air bags and onboard compressor. So, No sag or sway) No one adds a supplemental cooler. I did read the link about the bypass. It seems that just keeps the thermostat open at all time but it doesn’t actually allow more cooling. It gives full cooling immediately.
I'm going to make some assumptions here.
For an 8500 lb bumper-pull travel trailer with a properly set-up WDH, you won't need the air bags. It will squat your truck about 3/4" with the WDH set up. They're a waste of money for your rig. A WDH system is cheaper and faster than a fancy system like you've installed. Sure, with air bags you might look like you have no 'sag' or 'squat' but your front axle is still unloaded somewhat, so your steering is compromised.
With properly adjusted sway control, you won't have sway. Air bags don't really help with sway anyway.
No, no one adds a supplemental cooler when towing with a Power Wagon if they're staying inside specs. There's no need for one.
To me, I think you're trying to say you're wanting to pull this camper on just a hitch ball with no WDH or sway control - and that's just a dumb idea. I wouldn't want to be anywhere near you on the road, because you're not towing safely. You may not have a problem, but you're sure asking for one. For less than $500 you can buy and set-up a budget WDH and sway control and be safe.
It sounds like you're pulling a camper similar in size and weight to what I have. My '17 Wagon was ALL STOCK (no bypass, stock size tires, stock suspension, no air bags or other add-ons), I had my WDH set up properly and used a stand-alone sway control system, and had NO sway at 65 mph on the expressway (unless it was windy out). I had no issues with temperatures even after pulling big hills on a 4 hour trip north.
What I am saying is, get your WDH set up right, use a sway control, don't try to pull at 70+ mph the entire time, and you'll be absolutely fine.