IMO, we should pick our battles ... this issue seems destined for limbo in Congress, and has little chance of affecting our vehicles, unless the wording of the proposed legislation is very liberally interpreted.
But if we're gonna bark, I think we need to make sure that we get heard.
While there is power in individual letters, organized protest and lobbying are more effective. Get the 4wd associations to band together and promote a letter-writing campain and to hire or otherwise unduly influence lobbyists. This association should lend its logo, along with any others that we can muster, to a form letter published on the net that folks can print out and send to their Congresscritters. E-mail is usually not as effective as paper, so we need to make using the paper as convenient as possible to get the rank and file to actually send them. Provide links to Congressional contacts by zip code, for example. I encourage the Board of Directors to contact other associations and coordinate efforts.
But again, I think that we might be jumping the gun on this one, and should concentrate on land use issues while we can... we will never have such an easy go of it as when the Bush league is in power.