Put Armor All on the rubber and work it in, then soak a rag with Armor All and lay or attach it on the rubber overnight if possible. (What you are doing is getting it moist and plyable, because the sun is drying it out and making it crack). After doing all of this keep wiping Armor All on the rubber and keep it out of the sun as much as possible.
Hope this helps.
2002 Firebird Formula - 5.7 Liter