So now what? What's it going to cost to have it replaced? Jeez!
There is no belly pan under the water tank, and you did in fact find the acceptable jack points. Most older units do not have a "jack " label. I always jack under the steel frame member that holds the axles, just behind or in front of the wheel I want to remove. Just be sure to get it centered and if need be put a hardwood block in top of the jack, as some jacks may dent or bend the frame member if not accurately lined up. Also chock the opposite side wheels so the trailer won't roll or twist of the jack. As noted, you can pull one wheel off the ground with blocks under the adjacent wheel. I usually pull up on about two or 3 inches of block to take the pressure of the wheel I want to remove. That way the wheel is still on the ground to break the stud nuts and then raise it the rest of the way with the jack. Reverse to drop the wheel after installation so you can tighten the nuts and then pull off the blocks.
I have stated on forums many times, I will not jack up a tandem axle trailer of any kind nor use jack stands as they can and will slip. I have heavy duty truck stands and they have slipped. For safety I will only use ramps, wheels properly blocked. Blocks on stands in my opinion makes them unstable. Some one stated doesn't trust ramps only jacks. I hope he isn't under trailer if slips, if any one has worked is safety will tell you jacks can and do slip.
We have the same model Joe. If you look underneath near the stabilizer jacks in the back you should see the "Jack" with an arrow pointing to the jacking point. Look at this video. At 9:20 into it Patrick points it out:
2016 FC 25RTB
2016 Nissan Titan XD Cummins Diesel