Very cool 4x4 lifted Class-C.
It is tall already so not ideal to add to the roof weight, and we assume you go off-road some where top heavy is even less desirable?
I think the roof would hold the weight if spread out like you say, but you will be stressing the walls while driving, forcing them to hold straight while the water pushes side to side... I would be weary.
Trailers are prob out of the question bc you go off-road.
Look into getting a front hitch and use carry trays to carry water bladders there. Some trays fold up so when not needed will be less obtrusive. This will help on some trails. You can do the same on the rear hitch.
If you need to fold the trays to get down a rough trail then jugs work better as those can be stuck inside while you drive down the trail, but a giant bladder will be un-moveable.
Most hitches can handle 300-400 lbs.
I have a front hitch on my truck and love the expanded ability to carry things, usually a generator for me, and it is also a great tow point when you get stuck.
Also, no woman wants this advice, but maybe for you... I use kids shampoo when camping, it suds up way less and is much easier to rinse out. Raking as much of the suds out of the hair before rinsing will make it quicker to rinse too. Of course, you know, let the hair rinse be what rinses off the body initially.
One rinsed dish/pot full of water gets poured into the next pot to wash.
I can shower every day, prep two meals per day, wash dishes all on one gallon of water per day, and I get dirty when camping and playing, so is legit shower cleaning... You will have to minimize your water to save water for her. Sounds like she is at her limit for water saving.
** I just looked at your pic again. You have a custom front bumper, it might have a receiver already, but otherwise just weld one in.
Looks like solar on the front of roof so you are talking about the bladder near the rear, which is behind the axles, not ideal.
You could consider moving the AC unit to the rear vent roof hole (is the bedroom area?), and putting the water bladder smack dab center of the RV so you are not leveraging weight behind the wheels... lot of work to do this though
And you have stock size tires, so guessing not a lot of off-roading going on?