Don't be nervous. It will be fine - babies sleep really well in the fresh air (certainly after the first night). The travel cot will be ideal. It might be worth putting a sheepskin or something underneath the mattress for extra insulation from the ground. Her usual sleeping stuff with maybe a fleece all in one (you can get them in Primark or Trespass do a nice one with foldback hands and feet and a hood) and she should be toasty.
Bring some toys and a picnic blanket for her to roll around on and she will have a whale of a time. In some way, it is the perfect age as you know they will stay where you put them.
Oh and a tarp or folding gazebo so she can sit in the shade during the day(as, of course, it will be very sunny and will not rain, oh no). But as you are seasoned campers, you probably have all that sorted anyway.
It will be fine - its actually easier before they start moving Took DD at 5 mths, 6 mths and 7 mths - doddle, took DS at 10mths and just walking - arrrrgh, eyes in back of head job ALL THE TIME!!!
We used travel cot with DD to start with but seemed too draughty so put her on single air-mattress beside us. Very snuggly and dead easy for night feeds. Take extra blankets and buy fleecy sleepsuits to fit over jamas (though might have to wait until Autumn for these - Primark usually do them and I just buy next size up for next years camping!)
Mine are now 5 and 8 and LOVE camping - so much freedom.
Camping last weekend for first time with 4mo. I took our room thermometer and was surprised how warm it got during the night in the tent. Baby slept fine in carry cot, we took plenty of blankets but only needed them when he was outside, which he loved, just watching trees etc. I was nervous but it was a lovely experience. Are you BF? That takes away loads of stress as we were camping with a couple whose baby was FF and needed warm bottles! They were campstoving at 3am in the pitch black! eek