Thinking about camping here end of March. Is it open? Will it accommodate a larger 5th wheel?

You will probably want to stay inn Columbia Falls

Yes in Tourism Sites There are always Places to stay, I say to stay. Hope this helps. Boa noite

Yes, I think that the end of March is a good time. I went in July and it was very good too. ✌️😄

You'll likely need to camp outside of the park as the snow will still be covering much of the area. Additionally, plowing efforts on the going to the sun road don't start until at the Earliest, end of May