I use the single tire covers, they are canvas, not vinyl, so they wont crack.I got them 4 in a package from Harbor Freight for around $13.00, and thats for the 4 pack not just one or two.
They hold on with a spring type wire on the back of them and they fit perfectly on my 15" tires. My neighbor has used them same kind for a few years now and has not had 1 fly off from high winds and being by the lake we get some pretty strong gusts.
Brian, Tamara, Abigail
2003 Lincoln Navigator Ultimate Edition 4X4
2004 Crossroads Cruiser CT30RL