Protection against flat spots on tires

I've just put my car away for the winter and want to buy something similar to these tire protectors that are sold by Holden in the UK. I've Googled unsuccessfully. Are any of you guys familiar with these in the US and if so who supplies? I can buy them in the UK and get them shipped but freight will cost as much as the item.

Thanks

http://www.holden.co.uk/displayproduct.asp?pCode=095.175

I put the Tiger up on good 'ol jackstands with a bit of wood between stand and car.

Something like:

http://www.tirecradle.com/

http://www.amazon.com/s/?ie=UTF8&keywords=tire+cradle&tag=mh0b-20&index=aps&hvadid=3527265254&ref=pd_sl_7ii8zzfr59_e

I use my car dollies that have a curve to them. While I have to jack the car up to put them in place it only takes a few minutes and I can move the car sideways etc.

I find them a bit easier than jack stands and the weight still sits on the suspension the same as tires on the ground

I also air up my tires to their maximum inflation ratings

Same here the cheap dollies from auto zone work great.

Worst case get some thick Styrofoam pads (2 inches). The tires will push them in with the weight of the car, so they will get a curve that cradles the tire. This is only a makeshift solution but it kinda works. I'd get some tire cradles like the ones posted above.

Also I would not use jack stands on a convertible. Cars are designed to carry their weight on the suspension points and a convertible will probably flex over a period of a few months on jack stands. (Unless you have subframe connectors and whatnot to add strength)