It is common to tip for service while traveling. From bell boy to barman, they make a living by serving you well. The tour staff; driver, mechanic and ride director are all part of the tourist trade and you will be well taken care of by this team. It is not mandatory that any tourist tip any worker but people are always asking for guide lines and this is what I do myself while travelling. If my room is clean and tidy with towels etc. In place, Then I will leave $1 on the bed in the morning, this is travel etiquette shall we say. As for the ride staff a gratuity of around $30/$40 is common for a two week ride or $2 to $3 /day. We prefer you tip directly and individually to each employee.