Writing a thank you note to a pallbearer is never an easy task. The occasion for his participation as a pallbearer demands a certain level of care and consideration as you construct the note. It is always best in these situations to keep your note simple and straightforward. Simply thank the pallbearer for his help and support in your time of need.
No thank you note can or will properly demonstrate the weight of the situation in the wake of a death of a friend or family member. These services and funerals take an untold toll on family members and close friends alike, and they would be nearly unbearable without the support and help of friends willing to participate. When writing a thank you note, let them know how much you appreciate their willingness to help.
Do not stress about the length of the note; say what you need to say as simply as you can and then move on. A small reference to the value of the pallbearer's relationship to the deceased is certainly welcomed, but it is not always necessary. A small portion of the note can be dedicated to wishing the pallbearer well in his ventures until you see him next.