Just on the tyres, I must admit I hate officialdom & kick back when I can, but I do believe that trailers over a certain weight ought to have some form of MOT test each year, which tyre age would be a factor. That way the dealer would probably by law have had to have changed them for you, mine need changing this year, but as we're having a extension on the house not even sure we'll get to use it until the back end of the year. We've had it 3 years & I've never looked at the spare, I suspect it may even be an original from 2002.