Thanks. I was reading that for long periods of time outdoors I should put a cap on the antenna connector and take the connector off. Is this true?
The NMO mount itself has an o-ring seal under the mounting ring that will protect the vehicle. Good antennas will have an additional o-ring on its base, that will add an additional seal. No reason to use an NMO rain cap unless you specifically need to remove the antenna for long periods of time. Even a short run through a car wash won't harm an exposed NMO mount.
Also, can you point me in a good direction to get quality parts and/or instructions? I don't wanna mess this up lol.
A couple of things...
Avoid the Cheap Chinese Crap. There's little cost savings. Spend the extra dollar or two and go with name brand mounts. Larsen is my personal favorite. I've been using Larsen for well over 30 years and never had one of their mounts fail. Do —not— buy the cheap Chinese mounts, Tram/Browning or the ham radio specific brands. If you are going to drill a hole in an expensive vehicle, install a suitable mount, not the least expensive one you can find.
The mount will come with directions. Follow those.
Spend some time figuring out the locations. You do not necessarily need access to the underside of the NMO mount. They are designed to be mounted "blind". Removing the headliner is rarely required. I cannot remember the last time I ever had to drop a headliner on a vehicle. If someone tells you that you must drop the headliner, walk away, they've never done an NMO install.
Consider the antenna locations with regards to providing suitable ground plane under the antenna. Ideally you want 1/4 wavelength in each direction under the antenna. Consider suitable antenna separation between antennas if one or more are used for transmitting.
Use the correct tools for the job. You will absolutely need a 3/4" hole saw or chassis punch. NMO specific hole saws are a tad expensive, but are designed with a depth limitation feature. It really is worth buying the actual NMO hole saw. However, I have used some 0.750 diameter hole saws that were designed for thin sheet metal. Home Depot has one that I had to purchase in a jam, and it worked really well. I think it was a DeWalt brand. Don't use hole saws designed for wood. Teeth are too aggressive and can get you in trouble.
Get a piece of scrap sheet metal and make a few practice runs. Get the feel for how the saw bites in and how much pressure you need. Don't overheat things, go slow, you've got plenty of time.
Good NMO mounts will sometimes come with a small tube of silicone grease. This is to be applied to the O ring that goes on the underside of the NMO ring when you install. The grease is to keep the O ring from binding as you tighten everything. If it doesn't come with it, not a big deal, but using a bit of suitable grease is good practice.
Use good antennas. The Larsen NMO mounts that use the black bases have an excellent sealing gasket that seals the underside of the antenna where it mounts to the NMO mount.
EM Wave has an equally impressive sealing design.
Once you do one of these, and realize how easy it is, you'll be a convert. You'll also wish you'd done it a long time ago. It looks way more professional that mag mounts or compromise mounts.