I have been working in an idea for a trailer for our son and his family. With this size of trailer, I suggest you follow the build of Shawnee Hills Workshop. His off road trailer has some really good ideas for making a trailer of this size.
https://www.shawneehillsworkshop.com/The pop top and the shower will be greatly appreciated on a short trip, but really loved on a long excursion. A rainy day with 2 kids and the pop top might even save your sanity.
A few things I would consider changing, it is HOT here in Texas, so a good AC is not an accessory, it is mandatory. The shower, as discussed on another thread needs a base and waste water collection system. An enclosed vestibule/screen porch would also be nice.