I don't have a punt I'm afraid but as a teenager I had one, it was made from a slab of builders polystyrene insulation it was about 8 x2 feet and about 6inches thick. It arrived in our wood one day in a storm, I wrapped it in packaging film like the stuff you get on pallets, only really to protect the environment from bits coming off if you caught a submerge tree. Longest distance it covered was about 10miles but quite light to transport if needed. Just an idea that might help.