I'd spray on some epoxy primer and top that with some chassis paint. I used POR-15 on my 260z and wish I hadn't.
Its such a pain to work with (mess and smell) and it has peeled off in areas where I had used it over galvanized metal.
I used epoxy primer and chassis black paint from Eastwood for the underside and I'm real happy with the results.
For the interior, primer by itself should be fine. I used a cheap touch-up gun from Harbor Freight to apply.
http://www.eastwood....it-gray-qt.html