Auxillary Fuel Tank ?

In the past I have had a few trucks with auxiliary tanks. (First F-750 carried 150 gallons between back of cab and winches) All had a manual valve to switch from tank to tank. But back when those trucks where built one line went from tank to pump. Vent was another line, or hole in cap, that just went to outside. My '85 Fords with 2 tanks had a electrically controlled valve, with a hole bunch of lines. My old Dodge half ton, I have thought about a tank in the bed. But don't want that many lines thru the floor, to much chance of issues. Thought about just pumping fuel into the neck of stock tank, but if I open the fuel cap the engine will die. (On a lot of gas vehicles a loose cap will turn on "check engine") Then I decided to just pump gas while I was stopped, take break not at gas station. But finally got the idea between my ears; I'm retired, no longer need to stay between the doors every minute I can. Stop when I want, and pull into a station about every 300 miles.