Time to chime in. Dude has a Rocket III TOURING <== key word, TOURING. As in getting out and riding around the country comfortably and looking at things other than the next bar or 1/4 mile strip.
Stopping around 150 miles or so for gas on a Touring bike is just aggravating.
I did a lot of LD riding on my R3 Standard and it is not an appropriate mount for that kind of riding. So I bought a Trophy for the serious LD rides and rallies.
I fitted a TourTank to the Trophy to extend my range up to about 400 miles between fills. Yeah, I can make it without having to stop and pee every 100 miles.
I had a quick disconnect mount made that allows fitting in about 10 minutes. The tank mounts above the rear seat and is a gravity transfer type. When the low fuel light comes on for the main tank, I reach back and turn the valve to refill the main. Takes about 10 minutes to transfer 4 gallons back into the main.
A TourTank could be easily fitted to the luggage rack of an R3T. They are not expensive either.