Planning to ride up to NH next weekend.

couple newbie questions
1) What are the recommendations for security while camping? Is it safe to leave tent/sleeping gear and proceed to the top lightweight? Any storage/lockers available? Or just leave heavy gear in the car, hike to the top, come back to the car and hike back up Tuckerman Ravine trail to establish tent/lean-in area?

2) Lean-ins - are those just public shelters for multiple people or those are semi-private? Also, do do those get reserved before tent sites? It would be nice not to have to lug tent around, if it would be known that lean-in area is available.

Thanks in advanced..