Go NMO
I buy them by the gross, 2 or 3 times a year. There are brass and stainless, 1GHz and 6GHZ models available, and every flavor of coax known to man- coax choice is more critical than anything else. Don't buy the pre-installed coax connector.
Don't pull the headliner down. Pull (hard) on the upper door seal, and peek under the headliner to find a spot where you don't drill through a stiffener or roof brace. The door seal will go back and reseal fine. Don't pull more than you need for easy access.
Tape measure the center of the roof. Use the inside of the door frames as reference on both sides- car builders don't always get their roof seams straight. Measure and check twice, drill once. Re-check for stiffeners and braces. X marks the spot.
If you are installing on a newer pickup, pull the third brake light out of the back and drill the holl as far forward as you can. 4" from the back tunes fine on VHF, and higher freq's won't care.
Drill an exactly 3/4" hole from the outside, but don't go too deep and into the headliner. If you borrow an electrician's s hole saw, make sure that it will drill a 0.750" hole, and not a conduit-size hole. If you don't have a $150 carbide antenna install hole saw, wrap the outside of a home store hole saw with tape and keep the pilot short to save the headliner. Don't panic if the hole saw wanders just a bit. It's only paint, and the mount will hide it. Watch out for the piece, it's HOT, but not hot enough to damage the headliner. Pull it out lest it rattle for the next ten years.
Get a 3' piece of 1/4" nylon tube (ice-maker water supply tube works great). Put the tube in the hole and work it straight sideways to the door. Have a flashlight handy, and a coat-hanger to reach the nylon tube when it bends the wrong way. Don't panic if you bend the edge of the headliner a bit- they're self healing.
Plain old electric tape will work nicely when you slice a finger open and are bleeding all over the car.
From the hole, slide the coax into the tube an inch or three and put a single wrap of the aforementioned electric tape around it to make sure it stays put. More wraps will find something to catch on. GENTLY pull both through, exiting between the headliner and door frame.
Leave the tube on the coax. Finish the NMO mount, and use the tube to work the coax behind the door seal(s) to the radio (keep it behind side airbags!). Stay in the roof and run down the A-Column to get behind the dash. Tie the coax clear of steering U-Joints and size 14 boots.
Remove the coax completely and do it again, this time without being wrapped around the wrong side of the door seal. Cut off the excess, install the connector (use solder above VHF or 45 watts), install the antenna and tune it, and go to the next car.
The only times I've had a leak was when I thick-fingered the O-Ring, or had to re-use an existing hole that was bigger than 3/4".
Water is not your friend. Antennas come with a packet of silicon grease for a reason. Use it under both mount and antenna O-Rings and on the outer mount threads. The silicon also keeps the edges of the hole from rusting, making for better contact. Remember that the roof is the other half of the antenna. Some antennas come with an adhesive circle that goes around the mount and sticks to the roof- if the paint is rough or oxidized, it will seal to the roof and give a smooth top seal for the O-Ring.
I never use backing plates, but I do make sure the inside fingers are fore and aft, and stay that way when I tighten the outer ring. They make a special tool for that, but a pair of needle-nose pliers works just fine. That makes the antenna less likely to fall off when (not if) you find a tree limb.
Roofs more than 3/32" thickness require two sided installation mounts, and access to the underside of the antenna. Most car and truck roofs are less than that unless you accidentally find a #$%$#! stiffener.
The center contact of the antenna is critical- make sure you get it right the first time, and unscrew the antenna annually and check for good contact and water.
There is an NMO base antenna available for every frequency and application.
When you trade the truck in, leave the mount and coax for the next guy. That will save both of you time, money and trouble,