I used POR-15 last year when repainting my Cabrio chassis. I used the grey colour (three coats, I think, working on smallish areas at a time) and then put Chassis Black on top. The POR-15 does seem remarkably tough (I've got various suspension bits that have POR-15 on them but haven't been top-coated) but I've chipped the Chassis Black on a couple of thinnish edges - made me think I'll put something over the top of that where stone chips are liable to hit.
As for coverage, I
think the coverage rates they claim were about right. You could have fun working out the surface area of your TVR chassis though
