Easiest trip planning software is Microsoft Streets and Trips. After planning, you can export it as a GPX file to the Garmin software Basecamp. Basecamp allows you to modify and/or load it into your GPS.
Plan each day as a separate file/route and store it in your GPS this way. Each day, load that day's route and you are good to go.
As an alternative, if you are just interested in getting from one location to another (without micro-planning the roads being used), just load the ending point of each day in the GPS. At the start of the day, set it as the destination and follow along.
RR