This is an unusual request, but I’ll do my best! Will you be in the outdoors a lot? Because the most off-the-beaten path locations will probably be outside. On that line of thought, my first idea is Mt. Ashland. Any time of year, the Mt. Ashland access road is accessible, and in spring and summer, it’s possible to hike and picnic up there (or ski in winter). The historic lodge will not be open in the off-season, but if you drive to the end of the parking lot and drive or walk up the dirt road, you can get to a nice trail that leads to the summit (you hike up the back). It’s a beautiful spot for a proposal, and only about a mile hike.
Otherwise, another nice spot is Lithia Park in Ashland. It does get crowded, depending on the weather and day, but if you go to the top of the park (park above the playground and walk up the trail), the upper duck pond area is rarely crowded. In the summer and fall, the stand of trees across the street from the upper duck pond is a nice area, too.
In the Applegate area, any of the wineries on the Applegate Wine Trail are scenic, and often not crowded. It would be easy to take a walk from the tasting area into the vines for a proposal. Hope this helps!