Q: What cover is 100% water tight?

The covers that wrap over the sides of the bed are always the better bet as far as keeping the elements out because the water rolls off the sides. Although there are some good products that are retractable and folding which can be fine tuned to be in the 99% range. Usually a small amount of water won't hurt anything in the bed if you have a drop-in bedliner because the water will sit in the creases of that liner. You should never have an issue with any cover purchased from Joe's Truck that is just letting water poor in. All the brands we carry are top-notch manufacturers

Q: Should I buy rain guards that go inside the channel or stick on the outside?

We always recommend getting the in-channel rain guards by Weathertech. They use NO tape and fit great. With rain guards that stick-on you have all the elements to attack them and if(when) you have an issue it is always a mess trying to remove the old tape to reinstall new ones. Weathertech is the way to go for sure.

Q: What kind of bedliner should I purchase?

Well you have (3) choices in our opinion; drop-in, spray-in, BedRug.
DROP-IN - If you aren't going to be keeping the truck for long, if you don't use your bed for any heavy use, if your getting a tooneau cover or if you just don't want to spend much on one are all good reasons to get a drop-in liner.
SPRAY - If your planning on keeping your truck for a long time, 5+ years, using it for heavy duty loads, or just want a custom fit look the Line-X liner is the way to go.
BEDRUG - If you are getting a tonneau cover and want a custom look that functions great, keeps sliding down of items in the bed, keeps bed noise to a minumum and can be slept in comfortably if you get kicked out of the house after buying all the accessories for your new truckā€¦or go camping, then the BedRug is the way to go.