400lbs is no joke to move around over soft sand. Wheeleez larger wheels will just float it over the sand. If moving a long distance a front dolly is really nice to have. I had a 4.2m Zodiac with a 40hp that weight just over 500lbs. I could solo launch, but needed help getting back out. On a steep beach it took a minimum of 3 people, with lesser beaches requiring 2 people.
I used Wheeleez 49cm and built my own legs. Now Wheeleez offers a 42cm wheel with legs for a chunky sum of $500. Not much else will float your boat across the sand though.
https://wheeleez.com/product/wheelee...h-42cm-wheels/
You might also need some kind of pump, be it manual or electric to drain the boat should it take water onboard. It happens when in the shore break. The Pacific will always find ways to throw the unexpected at you.