The trouble with ArmorAll is that it contains an alcohol component and that does indeed eventually dry out and crack rubber. Silicone sealants work well but do evaporate over time. Plus they are usually quite thick and gloopy and can make a bit of a mess. Formula 2001 works pretty well and doesn't seem to dry out stuff.
There are also some UV sprays available that you may want to consider. I'd coat the tires with a liberal amount, let dry and repeat. From there, you could probably satin or flat coat them if they needed it. Rubber isn't as durable as resin or styrene, but it does add realism. You may want to keep the rubber set available for competitions etc. and use the plastic/resin ones for normal display. Then you could keep the rubber sealed and out of sunlight in the meantime. Just a thought.
B~
"I may not fly with the eagles.....but weasels don't get sucked into jet engines!"