50 gallons of fresh water in our Eagle Cap.
But as far as storage for all your gear- THAT will be a rude awakening coming from even a short class A.
Example- quite a few years ago we had our first truck camper. Then as our 2 kids grew we went to a travel trailer. Forward a few more years and they wanted no part of an RV.
At that point we traded back to a different truck camper, but before the trade in I emptied the trailer contents onto the garage floor. WOW- what a mountain of stuff. No way would 1/3rd of that fit into the new camper, even considering that we always try to keep an eye on weight.
Good luck!