SFX question

[Breakdown]

Upon rewatching Mothra vs Godzilla, I'm extremely curious to know how they made the Lightning towers and Tanks melt under Godzilla's heat ray. I'm aware that in the first film the towers where made out of wax and where melted under studio lights, and that might be the case here, but how did they make the Tanks melt?

[PRIMEVAL]

They may have been out of something like plastic, which burns when set on fire (if I remember correctly, the melting tanks did have a flame on them).