Knotty, I've been out of touch (camping up in Colorado) so I'm a bit late getting back to you.
My fresh water tank is just behind the front of the trailer (and I suspect this is where most of them are). In my trailer, this puts it about halfway between the hitch coupler and the trailer axle. So, filling it with 300# of water, adds about 150# to the tongue weight. Before the axle was moved, it was more than halfway to the coupler.
After weighing things with the original setup. I used the things I'd learned in college regarding weights and moment arms and determined I could move the axle 3" and it would help a bunch.
The trailer tows beautifully now.
- Jack
