you'll have a lot of options, and yes, there's no reason the outlets in the truck, which draw from the truck's own battery, wouldn't be available while charging - just like when you get in your truck to turn on the radio, or video, or heat, or air conditioning, while waiting for charging - the inverter should always be active when needed.
I think the idea of 'camping' with these new EV's are fantastic, too, as I'm a long time camper owner. I can see pulling into the campground site, and plugging the truck into the 50amp 240v outlet, and then plugging the camper into on of the 20v outlets, or even using a 'Y' adapter to plug into TWO of the truck's 20amp outlets - if one or two are not already available on the same campground pedestal as the 50amp outlet, which most of the time are.
If the campground has only 30amp 120v power, then do the same, or, if you wish, plug the camper into the 30amp outlet and the truck into the 120v outlet, etc.... each option depends on the situation, the campground electrical options, and how you want your time there to go.
If you want to 'off-grid' camp, no problem, just plug your camper into your truck : )