Using aux gas tank as main gas tank

[JerryIndy2112]

I have a '71, GMC, 1 ton. It is the custom camper version. It was sold at dealership with a camper on it. It has the main fuel tank behind the seat. It also has a fuel tank under the bed, drivers side. Has anyone used the auxiliary tank as a main and removed the one behind the seat? Fuel tank sender to see fuel level? Replace aux with new and better tank with a sender? I am planning right now. But would love the extra space. I do not have key to aux fuel door. Would love to weld in a square body door to open and fuel. I have picture below. Give me your thoughts and experience.