eccj, you can just use those little ones on the grate, about $5 even at a regular grocery.....
a possible downside might be you don't really know where you're at at a moment's notice without lifting the lid.........forces you to trust you're setup more, but does give you a reasonably decent read on what's happening right at the cooking area..........
i use them to figure where I'm at, right at the start & at the times I might go to pop the lid & check things anyway...........
Lance (Mirkwood) uses that Maverick to great effect......i saw him work with it at the meetup we did awhile back & you could tell right what was going on at any given time......i believe also, that there are some less expensive options of the same type setup (meat & grate temps, both), just that Maverick's a trusted, reliable make in the field...............
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