All excellent advice! Be sure, as billk says, that you've matched the type of sealant to the waterproofing of what you're sealing--silicone sealant (Silnet or diluted GE Silicon II) for silicon-coated and the other type for polyurethane coated.

I discovered the hard way that it's not a good idea to seal a tent on a hot day; the mineral spirits evaporate too fast and you have to redilute the solution every few minutes. The garage (if open while you're doing it) might be a better idea if it's warm, assuming you don't mind leaving your car outside overnight.

You don't need to coat the floor except to seal a seam if it has one. You need to be sure you don't pitch your tent in a place that will become a pond in a cloudburst no matter what kind of floor it has or what you use (if anything) underneath it. However, if your floor is silnylon, it's a good idea to paint some broad stripes of the sealant on the inside to prevent your pad from skidding on the slippery floor. You may want also to paint a few stripes on the bottom of your pad. I discovered this the hard-way during a 3-week car-camping trip which was also a "shakedown cruise" of my lightweight gear. Every night I chased my Thermarest all over the tent every time I turned over. My dog got so disgusted with this nightly exercise that he resorted to curling up at the very foot of the tent, which is where he's slept ever since. He makes a great foot-warmer down there, but there are easier ways to train a dog!