Transmission temperature gauge

Thanks for the replies. I live in Texas so it is hot as hell right now. In July/Aug will be traveling to California, back across Oregon, Washington, Idaho, Montana and then back down through Wyoming, CO and back to Texas. It will be HOT Nevada and other places, so I'm a bit worried about pulling grade in many of those places without being able to monitor my transmission temperature. We always had a gauge on the pickups pulling our fifth wheel or TT, and so I thought I should have one on the Coachman. Also, I do want to take it to CO where there will be lots of mountains to traverse up and down.