I grew up in Eugene and used to take frequent trips to Florence, with our family we've been spending Spring Break going to Florence, specifically Honeyman State park for about 10 years with our ATVs. This year was the first time with our Jeep and our ATVs. Being new at it I didn't do so well on my first attempt getting on the beach, I should have air down more. But I'm not sure how well my stock tires would have done in the soft sand. That said, I've seen other Jeeps out there so no reason it can't be done. Few days later we went out to the end of South Jetty and made it out just fine.
The plus of Florence is you and ride the dunes, the flats and the Beach. You'll need to enter the Dunes from either Driftwood II or South Jetty that time of year. There are three entry points along South Jetty, one by Show off Hill, one near the flats and one down near the beach. If you follow South Jetty all the way out there is another entry point but you can only drive on the beach Oct-May if memory serves in that area.
To do any riding you'll need an OHV Sticker and an Orange Flag. I bought both at the Yamaha/Polaris dealer in Florence.
You can camp at Honeyman State Park but I'd encourage you to make reservations asap. This year we stayed at Woahink Lake RV Resort which is just south of Honemay but still has dune access and Woahink Lake is just on the other side of Hwy 101. This is a bit of a quiet, more adult, RV park, but it has full hook up's and it's not a wild party scene. Plenty of rules, but we had no issues. Given the choice, I'd stay at Honeyman personally.
It's a good base camp area, you can head north a couple hours with many things to do/see, and south to Winchester Bay and Coos Bay too.