My trailer, is plumbed for 4 100 lb tanks side by side that connected into a regulator with a 3 way valve. I could feed from the left tank, right tank, or both tanks at the same time. I usually run one tank, then switch over as needed so I could swap out the empty. No relighting when done that way.
I forget what the type is called but a google search and you will see many Co. that sell them.(dual regulator,dual tank regulator?)