Buy a ceramic fitting for the bulb as some plastic ones aren't suitable. Yes hang it in the tank but buy a guard (around £10) from your reptile store.
I'm assuming by dimmer you mean dimmer stat?
Just securely fix your probe just above the substrate in line with the bulb, if it's a glass tank maybe you can use high temperature mastic to hold in to the rear glass.
Set your stat to your desired basking temp and get a laser thermometer ( again cheap on eBay £15) and check your temperature hot, cold and ambient... It may take a day or two to get it set right.
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