IMBA is rounding up the troops!
It always helps to personalize e-blasts like this. I favor a short and punchy sentence or two, showing you have some knowledge of the situation but not taking up too much of recipients’ time. Odds are every single email is not going to be read, they’re just ballot-tallying.
What I said was this:
Please approve RIN 1024-AD72. Mountain biking has proven itself as an enduring, responsible sport. Opening national parks to mountain bikers will prove a boon to national parks, because the mountain biking community is an organized, committed body of resources that can provide considerable human energy, goodwill and work toward supporting and maintaining our wonderful national park system.