If you want to mount them under the parcel shelf, then a standard 90* style gauge bracket will work. They come in single, double and triple layouts and are pretty easy to get. Sure, they don't cover up the back of the gauge, but you won't be able to see that anyway.
I used to have gauges mounted under the dash rail to the right of the steering column and I wouldn't really recommend it as you had to go to effort to actually see the readout. I prefer my temp gauge in a prominent place, like right in front of me where I can't miss it.
