At the very least, Alito has the right enemies
Over at the Brady Center, the top three stories are about Judge Alito, or "Machine Gun Sammy," as they've taken to calling him.
Alito is also front-page news at the Joyce-Foundation-funded Violence Policy Center, where three of their four lead stories concern him (the fourth praises the San Francisco gun ban).
The Brady Center conveniently posts, at top right margin, a box where you can email your Senators. Just be sure to personalize the message!
I can see the reason for their upset. If a narrow view is taken of Commerce Clause powers, along the lines of Alito's dissent in the machinegun case, you never get to the second amendment. You don't have to get that far -- Congress never had the power to enact the law in the first place. That'd (probably) leave Congress with the power to regulate true interstate commerce. Require FFLs for interstate purchases, require FFLs to keep records, etc. But beyond that (viz., everything the antigun movement has sought since 1968, and all of their "boutique bans" on assault weapons, etc.), Congressional power is at the very least in serious question. So from their standpoint, Alito is a lost vote in almost all gun cases (replacing O'Connor, who was only a lost vote if the case involved a major conflict with State responsibilities).
And if a Court does reach the right to arms issue: in my experience, a jurist who is comfortable with guns is open to an individual rights view, and an open mind is all we need. The ones who are closed-minding are those who, at an emotional level, are frightened by private ownership of firearms. If Alito sees nothing disturbing about private ownership of full autos, it's probably safe to say he falls under the open-minded classification. So a probable outcome of him on the Court would be a vote both for narrow commerce clause powers and for broad right to arms understandings.