Those black metal bed caps like RSI and RLD get EXTREMELY hot when in direct sunlight. I know, I have one. You'd have to spray in at least an inch of foam insulation in the entire interior of the cap to even have a mobile air conditioner unit be able to keep up. Murphy's law, a system will fail at the worst time and when under the most strain (A/C unit unattended in high heat).
I assume you will be idling the truck and using the Pro-Power On Board to power the A/C? I'm not sure if I'd rely on that. (my dogs are in the back seat with the truck A/C running), 30 minutes max.
I use this:
Protect Your Property Around the Clock By Monitoring Temperature, Humidity, Power and Water. Get MarCELL Today and Start Monitoring What Matters to You
www.meetmarcell.com
and Ring dash cam looking at my two GSD's with a thermometer in view:
Help protect your car 24/7 with Ring Car Cam, the dual-facing dashboard car security camera. Two HD cameras1 with Night Vision detect and record movement, break-ins, GPS, and more. Get real-time alerts when motion is detected.
ring.com
Then I set my phone alarm to check camera every ten minutes as a two tier safety setup.
Of course all this relies on LTE so never leave your dogs alone in areas with no LTE signal.
Also the F150's have this stupid economy max idle vehicle setting that will automatically turn off the truck after 30 minutes. I haven't use my Pro-Power On Board enough to see if that over-rides it. That slider turns back on after you start your truck. I'll have to look into Forscan to see if one can disable that crap.