I now need to drag my 2.7m rubber ducky & 5 hp over 50m to the water with a bit of a short steep gravel slope at the water.
Any suggestions for good semi rough ground wheels?

Rolleez or Wheeleez are brilliant for going over soft sand or grass, they will even run over broken glass and not cut the tire. run them very under inflated, soft and squishy, not hard and bouncy.

Be prepared to pay through the nose since the $AU crashed big time. I used to bring these in from the states for various projects ... but no more.

beachwheelsaustralia.com/product-category/wheels/polyurethane-balloon-wheels/

Wow they are pricey and possibly more than I need. Thanks for the idea.
Any other suggestions?

I have these on my 2.7m inflatable with 2.5hp. They work well across pebbly beaches (do need to clean pebbles out every now and then) and soft sand.

www.whitworths.com.au/yachtman-s-dinghy-dolly-wheels