Most tyre manufacturers recommend changing less used tyres every 4-5 years. The year of manufacture doesn't necessarily tally with the length of time on a vehicle. Old tyres normally degrade at thinnest part first and this is the sidewall.
If it was me I would be changing them even if they look ok.
We had our 2000 Pennine serviced in 2012 and the guy said we needed new tyres. I explained that they had loads of tread which was somewhat over ruled by the fact that our tyres were 13 years old and were cracking! Etyres sorted the issue but a lesson learned.
Before getting the camper and now caravan I'd only ever changed car tyres which I wore down within a couple of years and hence never had to worry about the age of them.
Bought a brand new Camp-let in 2011 and the tyres on it were 2008! Changed them this year even though there was lots of tread left and they looked ok. The M6 is no place to find out.
You not only should be looking for cracks in the sidewalls but also between the treads.
I experienced this last year, the tyres on my Pullman had already been replaced, they were 6 years old at my inspection.
No sidewall cracking, but there was between the treads.
New tyres put on, better safe than sorry!
------------- I came into this world with nothing and I've still got most of it left.
You could take the wheels off at home and just take the wheels in to Kwik Fit. I don't think I fancy trying to reverse a trailer in or out of my local Kwik Fit and they get a bit funny if you suggest they jack the trailer up outdoors.
If you can take them off at home it makes life a lot easier.. Although Kwikfit only seem to have one R13 tyre.. I paid £44 for one the other day. I'm going to the local BlackCircles tyre place to get a price for the other 2 (and maybe a better spec of tyre).
Anyone ever used Maxxis tyres? Looking at these all season tyres £30 and XL rated so load rating of 83!