I understand the issue...a 250 mm pier would be strong enough no doubt but it is the "fitting" ... I could walk you thru casting one in alluminium to fit your current bolts if you like
We had a thread recently as to what would be left in a thousand years ..I vote your slab and piers
You wont believe this...not withstanding a clear afternoon I now have clouds...and I went to take some flats but I have lost the little power pack...yes in a small caravan it's bound to happen.
Alex