Covering tyres!

I was talking to my caravan service chappie not so long ago and as my van is 5 yrs old now, the conversation turned to tyres. He told me that I should really change my tyres after 5 yrs as the UV light will have attackled them. I told him that my tyres are permanently covered when in storage and when on site- one with the awning wheel cover and the other with the bog standard covers available from Protec and Specialised Covers etc. He was surprised as not many if any do that and said that with that history they should be OK for another 2 years when I think they are changed regardless? ( that's what he lead me to believe anyway). So, there is money to be saved by taking the simple step of buying wheel covers and using them. They are not expensive and are usually supplied with covers these days. Looking around my storage facility they seem to be as rare as rocking horse poo as I only saw one other vehicle with them fitted and it's a large storage facility. Tyres for caravans  are not cheap- covers are so use them and save money.