For aluminum and steel internal floating roofs, double shoe seals are becoming "hot", liquid mounted log seals are "cold" and wiper seals are "cool". Sleeves around gauge poles are becoming common as are floats inside the gauge poles.
Foam seals are basically a cotaed fabric bag surrounding a urethane type foam that is squeezed into the space between the floating roof and the tank shell, usually halfway into the liquid. Mechanical seals utilize a segmented band of thin gauge steel plate pressed against the tank shell by some mechanical linkage and springs with a coated fabric attached between the steel plate and the floating roof.
Leakage inside a floating roof is hard to fix in service due to the hazards of the confined space. Since leaking often reduces buoyancy, the floating roof may sink or hang up. Take the tank out of service QUICKLY !!