Glad you asked your question! Crater Lake is gorgeous in winter, and yes, March is still definitely winter there! Right now, you can still snowshoe, and I do recommend it; this is a great way to see the park in winter.
If you’re coming from the Klamath Falls area, I suggest you check out this Travel Oregon story (full disclosure, written by yours truly), which outlines itinerary ideas.
It’s written specifically for family adventures, but can be applied with or without kids in tow. For a guide, I recommend Roe Outfitters (in Klamath Falls) if you want a tailor-made day in Crater Lake National Park just for you. We have spent time with Roe and they’re fantastic.
You can also sign up for snowshoe tours directly at Crater Lake, provided you visit on a weekend. Go here to find out more. This is a great budget way to explore the park and be guided by a ranger.
If you’re snowshoeing on your own, and want a GPS tracker, I recommend the InReach or SPOT. You can see a comparison of the two here.
Always check for park closures and road closures before heading to Crater Lake in winter. I see that right now, the south entrance (which is usually open in winter) is temporarily closed due to heavy snow. Check here for updates.