If I were doing it, I would ask for several things to be written to make sure both sides understand the terms.
Here are some things to think about:
When are payments due and in what form - money order, paypal, check ,etc
What happens if I have to cancel - do I get any $$ back? If not, can I reschedule my vacation (or rent the points to someone else) and if yes, how long would I have to do it. In other words, when do the points "expire"
When will the owner will send me a copy of the confirmation letter.
How can I confirm the reservation later on
I would want owners name, address and TN in addition to email. Would be helpful to know when the best time to contqct him/her would be.
References - Have they rented to others that would be willing to trade emails with me or talk with me on the phone?
Anyway, that should get you thinking.
I don't have the link handy, but there are a few sample contracts that you could look at - maybe someone else will post it for you.
Best wishes -