By March, we lamb everyone outdoors but if the weather is cold, especially if wet and cold, we bring in anyone who looks like she'll lamb overnight, or anyone with very very new lambs, for the night.
We're in the far north of England, so it is cold up here! But our ground has lots of reshes and other natural shelter, which the ewes make good use of, nestling their lambs in a clump of reshes or behind a hummock of tufty grass.
We do use the clear plastic macs for some thin-skinned young lambs if the weather is unkind.
We have foxes a-plenty but an experienced ewe is more than a match for a fox.
We only use iodine on navels when we have lambs born indoors, or coming indoors as newborns.
We bring hoggs and first-timer shearlings, or any other group where we could expect problems, in to lamb if we judge it best to do so - but lambing indoors can create its own problems so we'd always prefer them to do it outside if there is no reason not to, then we can bring them in once they've lambed if there are any issues to deal with.
Not sure where you are, Remy, or what breed you have, but if you're further south than us with a breed that has a decent covering of wool, the ewes have done it before, and there is some natural (or manmade) shelter, I would have thought they could lamb outdoors in April alright.
Hope that helps!
Sally