Erling raised that a few people were considering big wheel trolley upgrades.
The solution fitted to Harry's is (I believe):
http://www.allterraintyres.co.uk/index.php?main_page=product_info&cPath=1093_1319&products_id=4558
BUT YOU HAVE TO SPEAK TO THEM AS YOU DO NOT WANT THE SMALL BALL BEARING CENTRES!!! They can probably trace my order via "Sean McKenna" or maybe postcode "PO37 6RF" if you want to make sure you get the same (not the asymmetric version I ordered first and that is fitted to David Kast's boat - that is a more complicated conversion).
They gave us a discount for the ones fitted to Craigs boat on the basis of charity support but I am sure they would do the same for a bulk order if people clubbed together.
I also bought 2 x 1" x 10 SWG 3.25mm Wall x 900mm long Stainless Steel Seamless Tube 316 Descaled from
http://www.diamond-esupplies.co.uk/ for £45 plus £8 delivery.
Be aware that stainless is a bit difficult to drill if you are a hobbiest without all the gear and no idea but you do need the thick wall stuff or it will bend when bouncing down the beach!