We've been there many times. There is just something majestic about the lake. It's really a full one day trip or leisurely two day visit. I would camp at Diamond Lake or in Grants Pass. I think it's about an hour drive from Grants Pass.
You can use your toad to drive around the rim. There is a lodge and visitor's center. On one side there is a parking lot with a zigzag trail down to the lake where you can take a boat ride. It's a pretty good hike, so make sure you're up to it. There is no other contact with the lake.
If you stay in Grants Pass, you have access to either rafting or jet boating the Rogue River. The Oregon Caverns are also nearby and very nice day trip.
You could easily spend three to four days in that area and have plenty to do.