Anyone have experience with these Flatstoppers?

http://www.discountramps.com/flat-stoppers.htm

Do they work as advertised? What's on the bottom? I can see that they'd need some type of non slip material that works very well or else you'd have to fix them to the floor.

I'd like to know if there are any reasonably priced alternatives or even home made solutions.

I drive my SL600 about once per month. I have had issues in the past with my tires developing flat spots. I think the Flatstopper idea might be a good one; i.e. allow the tires to be much better supported than flat pavement as well as provide convenient easy use just drive on and off.

I'd be interested to hear of any experience with Flatstoppers or something similar. Or, if you have other ideas then that too.

Thanks

 

Ah I thought they were 259 each. They're 259 for set of 4. Ok then.