Hey it could work! I figure set up ashore at areas away from towns and populated areas, out in the wilderness, and have at least 5 guys well armed set up a small perimeter with makeshift barricades and machine gun set ups with one guy armed with hand explosives, send others out in groups of 3 like you said, one heavy arms/support gunner, one man armed with hand explosives, and a small arms man, everyone would have a side arm, preferably either a .45 cal or else a .357.
They would be sent out no farther than can be seen with a rifle scope and would forage the area, hunt, etc. When they came back all would have full body checks (the women would be checked by me of course
). then we would quickly break down the barricades and leave. I would set it up so that if everyone else turned 1 or 2 people left could set the place aflame and swim out. I would also bring a bazooka to take potshots at your island hehe.
That "hunk of crap" would be armored with sharp steel pikes about 10 ft long sticking out all sides except the one used for entry and exit, then sheet metal and kevlar would cover walls and such.