Simple sub and amp wiring question

It looks like I'm in a situation with basic wiring as well. I have one RF HX2 RFR3112 12" sub that I planned on using an RF 1000bd amp with. I'm putting it into a Miata trunk along with an 851X amp for my front speakers. I was told that with the single sub I would have to go at 4 ohms with that amp-500watts total, as opposed to 2ohms at 1000. When I told the RF dealer that I wanted to use ONE  HX2 RFR3112 12" sub , he told me the 1000bd amp was what I wanted. Can someone clarify. If you're getting old-turn it up so it still sounds the same-If you can't turn it up any higher -get a bigger amp.

I'D GET A BETTER AMP" RADIO SHACK" give us a break.Big Dave

no just kidding radio shack is fine if thats what you can afford. i would shop for a bigger amp you may find a good deal on the net somewhere.Big Dave