I have two tire tanks, and for a perment tank I would not use any thing else,
one is a large earth mover tire 8 foot across, and the other was "feed bunk" they had a guy come through here a few years ago and they turned tires inside out, I bought one from the local feed store and made it into a tank, in much the same way, it was old combine tire and the damage to it was on the side wall they cut off, I just poured concrete in the center,
our local FSA office or soil office had some prints if I remember, some places were selling pre cast "plugs" of concrete that would fit in to the rim hole,
on tanks that were being moved a lot I guess some were just using Benoite,
Rubber Tire Tanks - Wenzel Construction
some prints on the site above, in pdf form,
Giant Rubber Water Tanks
some directions and pictures of the setting on this site as well, in pdf as well,