No need to find an expensive bladder - you can get nice poly tanks at your local farm supply store that will fit in the back of a pickup. They are
light too, so you can take them out when not in use.
You know, you could do the same with a
battery pack - rig up something in a case to put in the back of your pickup to carry when you have those long
boondocking trips. I've thought about building something into a wheeled Stanley toolbox.
My new trailer is coming with 4 - 6 volt AGMS in a slide-out tray. These will be fine for my use for a few years. Later, I can see upgrading this to lithiums and save a few hundred pounds.
There are some folks running
air conditioning off an inverter in Class B motorhomes. Their
battery banks are around 800 ah. You can get a few hours out of that before the autostart on a
generator kicks in. To me, trying to make a system to run
air conditioning is just a fools errand. Just too difficult and $ wasteful for a variety of reasons. If we all had fuel cells instead of batteries and generators, then maybe.