If you put your general location into your profile it will help people give better targeted advice.
I don't believe that there is a special product for chicks. People make them from heating pads intended for people.
@Blooie is an expert on this.
Thanks for the tag…..I don’t know about being an “expert” but I have been using Mama Heating Pad for many years with great success.
@3KillerBs is correct. Mama Heating Pad is just a human heating pad arched over a scrap of metal fencing to form a “cave” of sorts, which the chicks use just as they would use a broody hen. They duck under when they need a quick warmup or if they get spooked, and as the sun goes down in the evening. It mimics a broody as closely as possible.
I don’t know what similar products might be available in Norway. But it’s critical that the heating pad be able to stay on continuously rather than automatically shut down after a couple of hours. Most of here in the States use the Sunbeam x-Press Heat heating pad because there’s a button on the controller that specifically says, “Stay On”.
Personally I can’t tell you what to do…..if I say “go ahead and use the heating plate outdoors” and something happens, I’d feel terrible. If I tell you to skip the plate and go with a heating pad and that doesn’t work for you, again I’d feel just as bad. Only you can decide what’s best for you and your chicks. All I can do is tell you what Mama Heating Pad is.
That disclaimer out of the way, I don’t see a need for you to buy anything more than the heating plate you already have. I know most plates do say not to use under 50 degrees F but 42F is not that far out of that temperature range and, as you say, they sure don‘t need it for long before they start weaning themselves off heat anyway. Check it regularly, and I wouldn’t put anything on top of it because you’re right, they do get hot. I think they actually get hotter than a human heating pad - I’d rather put a heating pad set on “high” on my body rather than have continual contact with the surface of a heating plate! A lot of people do use Press ‘n’ Seal on top of their plates. Shoot, I don’t even recommend that they put it directly on the heating pad, either.
I hope this helps.