i agree with them, thats a good idea of the crate with straw. guineas do good in quite hidden spots, an open ground will lead them to careless-ness. guineas when cooped, especially during their breeding season become quite aparthetically and careless they lay eggs on the floor other than in then nest boxes. and too with the fertility rate is quite low than freeranging birds, dont get suprised when you get less keets to hatching.
creating a well-hidden corner for nesting can be best. you just have to compare them to their wildness nesting range. in the woods they make their nest in deep rashes,grasses or beneath bushes. you can fake that too, to your coop by attaching a board against the wall and lay logs to blend it from your sight. i also use mowed grass as a cover. to live with guineas mean you need to explore their world a bit. when we cooped them for laying we dont place nest boxes or crates for them to lay. we creat shallow holes and line them with few straw, then cover it with dead or fresh branches with leaves. what i fear from them when cooped is - fertility rate. once hens are introduced to their new laying spots in the coop, at least she might have to bond with the nest for few days, then let her out when she laid 3 to 4 eggs. no more coop. A guinea has been tricked. thell come back every afternoon to lay in the coop for a day. thats how we do, to get the best healthy keets from trickey guineafowls.
best wishes...