My experience with my 2016 and 5th wheel were almost identical. I think the farthest I ever went when towing was 260 miles. By that point the "distance to empty" miles had long disappeared to be replaced by "fuel low". I was in the right lane and nervously waiting for any surging and if I felt anything I was prepared to immediately coast to the shoulder and add my 5 gallon jug. I made it and put a little over 30 gallons in; I really think that was cutting it too close.
I haven't towed yet with the 2020 (with titan tank), so will have to wait to see.
Like others, I am looking forward to the larger tank, and the flexibility of being able to pull into rest stops or tourist pull outs instead of scrambling to find fuel.
BTW, a little OT, but if you are not already using GasBuddy, I highly recommend it. We have saved hundreds of $$s by having my wife search ahead of time for where fuel is cheaper. In our experience, truck stops along the same route can be 40 to even 60 cents per gallon difference within a few miles.
B