I don't think there is any easy answer with a geodesic design tent. I have an older one, which is very good quality and I bought it to walk the West Highland Way, many years ago. As it happened I couldn't really have picked a worse time for the walk, as it rained more or less continuously for the whole 5 days or so.

You may be able to try and protect the inner by laying the outer over the inner, during the erection process, but I remember the horrors of putting the tent up outside the Kingshouse Hotel in Glencoe in the dark, in a howling gale and horizontal rain. In fact the wind caught the erected tent like a sail and it very nearly landed in the River Coe. I did get the tent erected, but then found my sleeping bag rather wet . At that point opted for B&B in the hotel as I was mentally and physically wrecked. At least I got everything dried out.

Using a tarp is extra weight, as said and in a howling gale is more trouble than it's worth.

I would never now buy a tent, which could not be erected flysheet first and tent designs have moved on, so I would think most quality tents these days would be flysheet first or both together.

I was thinking of taking this old tent geodesic tent with me to Norway next June, but given the likelihood of bad weather there, I may need to reconsider.

Grey Beard