You might or might not be Ok without heat. With only five you don’t have a lot for them to generate heat by huddling together. There is a reason the hatcheries have minimum numbers for shipping unless you pay extra for a heat source to be shipped with them. The most critical time is the first few days. It doesn’t take them long until they get where they can manage cooler temperatures, especially in a box to retain heat. The best way to do what you are talking about would be to build a hover, a shallow inverted box. Hot air rises. A box like that would trap their body heat in there. Just make sure it is low enough on the sides and not too high so the heat is trapped at their level. It doesn’t have to be really big either. You can prop it up on blocks or bricks maybe or hang it from the ceiling, but expect them to spend a lot more time perched on top than under it.
I’d feel uncomfortable trying that with only five and an overnight low in the 60’s. What I find that works best whether it is pretty warm or even below freezing outside is to provide an area where they can warm up and an area where it is cool enough. When you brood outside you get a change in temperature, it’s hard to maintain a steady temperature. As long as one area is warm enough in the coldest temperatures and another area is cool enough in the warmest temperatures, I find chicks straight from the incubator or post office are really good at self-regulating. At a week old, yours won’t have any problems self-regulating.
I use 250 watt heat lamps in the winter and probably keep heat on until they are five weeks old, depending in how cold it is. In the summer I use a 75 watt heat lamp and watch the chicks. During temperatures much warmer than yours I once turned the daytime heat off at 2 days of age and the overnight heat off at 5 days. The chicks told me they didn’t need the heat by getting as far from it as they could get.
To me it doesn’t matter how you provide heat, heat lamps, heating pad cave, heat plate, hover, or something else. What’s important is that one area is warm enough and another area is cool enough. Then watch the chicks and see what they tell you. You can try a hover without a heat source but I'd be nervous. Still, it might work.
