I think he is describing the semi containment device for the electric fuel pump or its pickup if the pump is external. Without a semi containment device for the fuel when a car corners and the fuel is lower. It could all slosh to one side leaving the pickup dry. Running dry might even just be damaging to the electric pump. I just am not certain.

This has been a fairly common item since electric fuel pumps came into common use. With fuel injection allowing air that is compressable to get into a highly pressurized area of the system may upset the applecart somewhat as well.

I forget the right name for those pots but they are very common. I never knew one to have a cover of some type though as well. Just an open fuel containment device with hole or holes to allow gas in and not let it get away too fast.

The urethane liner kits seem to be working out for quite a time now.If the tank is clean and not leaking do not bother lining it. If the device you mention has to have the cap on it you may have to cut a small area out of the tank and weld it back in to address this. The pot itself is usually spot welded to one half of the tank before the halfs are joined together with a rolling seam welder. It is not unknown for a pot to be loose in the tank but I never saw one with any form of a lid on it.