I like the multiple probe units made by springfield instruments. The coralife ones are cheap but very unreliable and inaccurate in my experience. I wouldn't risk direct sun in any case. Too risky, even if you're there to keep an eye on it. I'm not against it if your enclosure is made up entirely of screened walls and top, (no glass!) and if half the enclosure is shaded. During the summer I often put snakes outside in a screen enclosure to get some sun but you have to make darn sure there is shade for them and I don't do it if it's going to be a hot day.