the new DOT regulations 12yr etc.. are for portable 'BOTTLES'
yes they are steel, but the DOT calls anything that can be transported a 'BOTTLE'
'TANKS' are the frame mounted ones on MHs or than big thing on legs they are using to fill your BOTTLES
and yes, i would replace them
i only mention this because i ran into a 'grunt' that thought 'bottle' on the paper work pinned up at the fill location meant ALL TANKS, and did not know the distinction between portable bottles and frame mounted permanent TANKS
i know mos people call the 'portable BOTTLES' tanks,and this leads to confusion in some situations