Best thing to do is start searching for photos of other installs.
Be careful about the amateur installs, I've seen some terrible stuff. Instead, look at -professional- installs. Since Explorers were used in some law enforcement service, it should be pretty easy to find photos of good installs.
A good place to look is over at the BatBoards over at Batlabs:
Batboard - Index page There is a section of the forum that specifically deals with vehicle installs.
When installing, make sure radios are out of the way of airbags ( ! ). ALWAYS run your power directly to the battery. NEVER tap into existing circuits for any of the main power connections for your radios.
Permanent install NMO mounts for your antennas are the way to go, anything else is a compromise.