I want to add a faculty member to a preproposal but haven’t been able to confirm their interest since they are traveling. Can I just write them in and confirm with them later?

No. Please confirm the interest of all participants mentioned by name in a preproposal before submitting. If you are unable to get in touch with someone, you can note that you will pull in certain expertise from a person yet to be identified (e.g. – Chemical engineer with expertise in polymers – TBD).