Yeah, the blank plate (for the factory fog light switch that was an uncommon option) under the rear wiper/washer/defogger switches is a good place since it's made for a switch.
Some people prefer to use a protected switch with a cover in case their knee hits it or something. You may also be able to fit a pair of switches on there instead of just one, in case you want to control the lights as pairs if you're mounting more than two lamps.
Sometimes it's nice to be able to turn on just two lamps, or have a set on the brush guard on without having a set on the roof on, rather than only have either all the lamps on or all the lamps off.