Great project and write up. Hope to see further developments as you work out the details for phase II.
For heavy duty tent stakes, the 3/8 x 12" spikes, with a washer tack welded onto the bottom of the head works well in rough and rocky ground, packed gravel, and blacktop. An Estwing framing hammer drives them in medium ground, and pulls them fairly well. A 2 lb sledge drives them in packed gravel and blacktop.