My clipper has two tanks. Many clippers do - they were all installed aftermarket (2nd tank). Depending on how they are installed makes a big difference as to their benefits.
Some use the same intake and flow through one tank to the second tank. This means that the new fuel mixes with the old fuel when you fill. However, if you spring a leak, all the fuel is gone and the RV dead.
Mine has completely separate tanks with separate intakes. A switch on the dash determines which tank is used. I normally fill up both tanks before a trip. I drive on the front tank until it is about 50 percent. Then I switch to the rear tank and run it until I get to my destination or 50 percent. Then I fill both tanks again. This means I always have a half tank as a security measure. Because of its age, the rear tank doesn't flow well when it hits about a quarter tank so this ensures I use both tanks but have the front tank as my "going uphill rear tank issue" backup.
All that is great, but I could deal with one tank fine.
Where the 2nd tank has really come in handy is when damage occurs. When camping, a rock punctured my front tank and the fuel was gone. I was able to switch to the rear tank and get home on my own instead of needing a tow (after my trip of course).
When thieves stole my clipper, they slashed the intake line of the front tank to steal all the fuel. They didn't realize there were two tanks, so when I got it back, I was able to drive on the rear tank until I got that line fixed.
There's more to a good second tank than just "more fuel - fewer stops".