Looking for advice on best way To keep large toy hauler cool

The best way to keep a 43' toyhauler cool? Add that 3rd AC unit. :)

Seriously, the insulation in these trailers isn't the best by a long shot, and the main AC is just not going to do the job to cool the main part of the trailer. IMO the main AC should have been in the living area with some venting run to the garage. But even then it's going to struggle. There's a reason most big new trailers come with 3 AC's now.

Your wifes's idea will do just as you expect: you'll pump out the hot air near the ceiling, but that hot air has to be replaced by something, and that something will be air pulled in from outside: hot air. So you lose some hot air, some cold air, and replaced by all hot air. Not a good solution.

mrad wrote:
I will usually set the temp at 74 in the morning when the the outside temp is under 73 With the fan set on high.

Any other advice?

Set the thermostat at 68 overnight and keep it running 24/7. Get another bed cover if needed.

Vents closed unless you have just arrived with the interior at 100+. Close the vents when the sun sets.

A/C with a wall thermostat will have a freeze sensor to cycle the compressor. Sometimes these fall away from the evaporator allowing freeze up. Get in there and check it. Access by removing the inside cover.

While the lower cover is off check the plenum divider is properly positioned and sealed to direct all air to the ducting vs circulating internally. Poor installation methods are common. Get some tape and fix it.

Try not to park broadside to the sun. Any shade helps too.

I'm really surprised the OP only has 2 units. We have a 42' 5th wheel (non toy hauler) and we have 3 A/C units. 2 will keep things cool (we set the thermostats to 78°) until it gets over about 95°.

It's a 2015, guessing 2 was the standard then. I am considering running to COSTC0 and buying one of those free standing units that can cool 350 square feet and vent it out the window. Would be about 1/4 of the price of adding a 3 unit. Will 50 amp sites run three 15,000 btu AC's???

I am also wondering why the second AC went in the garage. It is seldom used to house people.

I'm not sure what size our 3 units are, but 50 amp RV outlets power all 3 + water heater + microwave.
Actually, we can run 2 on 30 amp with help from load sharing and solar.

While a 3rd A/C maybe your only solution. Insulation is what you are lacking.
My 39' unit does well with 2 A/C's. Granted my unit in not quite as big.
But I have an insulated ceiling.
Don't get me wrong my unit is nothing spectacular. It was slapped together like most RV's. But is does have some insulation and does pretty well in the heat and cold.
We have been good into the upper 90ºF in hot and humid Maryland and good down into the teens in the winter.
We generally heat with space heaters in the winter and use the furnace asw auxiliary back up.
In the summer 2 A/C's do the trick. I have never wished I had a 3rd.
I imagine adding insulation at this point may not be possible. But if you could find a way to add insulation it would go a long way.
Adding a 3rd A/C maybe your only solution but without adequate insulation it may still be struggle.

According to the manufacturer, we have plenty of insulation. The problem is the windows. We picked our RV off the lot and the RV came with single pane windows, lots of them. If we had ordered, dual pane would have been a priority - along with 8000# axles instead of the 7000# ones it came with.

Windows were my next question. Wondering if putting any of the anti-solar film on the windows would help at all. windows might make up 20% of my siding.

We've got the black roll up shades and we can feel the difference ( on the sunny side) between rolled up and down.
I'm sure solar film would help.

Definitely keep the roof vents closed.

The portable AC units probably won't help. At least the ones in the price range you are talking about won't help. They will exhaust out the window and then pull fresh hot air in from outside to replace the air that was vented out.

Do pull the center vent down on the interior of the coach and inspect what's up there. The AC is a sealed unit meaning it does not pull air in from the outside. Instead it pulls cooled interior in and cools it more and then pushes it out through the vents. There should be a divider up in the ceiling between the air coming in and the air going out. Make sure that divider is standing vertical in the opening and sealed with some duct tape to prevent air leaks between the two halves.

Buy a roll of good HVAC tape to seal inside the AC box in the ceiling. Do not use the cheap $1 duct tape. You want something like this.
HVAC tape