Tyre sealant gunge

Anybody had any experience of the puncture prevention stuff that you have put into your tyres. the spare wheel on our motorhome is underneath at the rear somewhere.  We have on of those skirt things fitted ( was on when we purchased MH ) so very difficult to get at. As the spare is in such a difficult position there seems little point in it being there if the sealant stuff works aswell as the companies selling it says it does. Any thoughts???