The white shell certainly helps.
You will need a minimum of a fantastic vent fan.
I would install low-e reflective window tint / insulation (Only reflective, no R value) to keep the solar
gain low. The main reason a car heats up so much in the sun is the huge windows
. Cars also have no insulation what-so-ever in most cases, and more often than not, the car isn't white. Keep the sun off of the interior of the trailer. Keep the vent fan on and the furthest possible window cracked open, and it will not get much hotter than ambient temp.
Also try not to park on hot black tarmac if you can avoid it, and always look for shade to park it. Not possible to park in shade? That brings me to the next suggestion.
I highly suggest getting a 100 watt solar panel
to keep the fan running at all times. You would then be able to rest assured that it will operate so long as the sun is shining (which is exactly when it needs to be working!) without damaging your battery
. You can mount the panel on the roof horizontal and it will still be plenty efficient to run a fantastic fan vent.
Gila LES361 Heat Control Residential Window Film, Platinum, 36-Inch by 15-Feet - Weatherproofing Window Insulation Kits - Amazon.com
that is EXCELLENT;
Amazon.com : Renogy 100W Mono Starter Kit: 100W Solar Panel+20' Solar Cable+30A PWM Charge Controller+Z Bracket Mounts : Patio, Lawn & Garden
This panel is a small price to pay for peace of mind. Not to mention that it will allow you to keep your furnace
operational for the chilly nights you may experience as well as charge electronics etc. You said you will often be without hookups, so I think it will be invaluable. Each panel has the added benefit of shading part of the roof from the sun. They should be mounted up above the surface.
Depending on what your budget / need is, you can install enough of these panels to actually run an AC reliably. If you want to go the AC rout without spending nearly this much money you can use this generator
Amazon.com: Earthquake IG800W Model 11613 Portable 800-Watt Inverter Generator with 40cc 4-Cycle OHV Viper Engine (CARB Compliant): Patio, Lawn & Garden
Along with a 1500VA Uninterruptible Power Supply to run a ~5,000 BTU AC.
The UPS handles the surge load. When the compressor kicks on it trips the overload on that little generator
, which then switches to battery
backup. The generator auto resets, which then triggers the UPS to switch back to it. That generator can run a 5k BTU all day even in extreme heat. It only fails to start the compressor since that requires a large surge of power.
Good AC for this;
It has flash memory so there is no worry that it won't come back on after a power interruption. Up until these more recent models I avoided digital AC units for this exact reason. Ferrets HATE heat, and I can't be having them roast because of an AC not turning back on!
That's the lowest cost and most simple method of having AC you can count on for your dogs. That generator has a vacuum diaphragm powered fuel circulation pump so it will not vaporlock in hot environments.
Because your animals lives are on the line here, I would suggest a monitoring system that will send an alert to your phone should the system fail for any reason.
One more idea! Evaporative cooling can be made to run on that solar panel
extremely easily and cost effectively. This will only work in dry climates. However, if that's what you are dealing with then you can easily keep the trailer at 70 degrees even when it's 90 out.
If you have any questions about the suggestions I have made, or anything else let me know. I am more than happy to help.