I never seal my DIY tents
Pyramid so they have steep walls. Flat felled seams. I have used them in lots of rain in PNW. I camp in winter. Cheap silnylon that's not very waterproof.
Occasionally, in heavy rain, I'll feel a little "misting" which is enough to feel on skin but not enough to get things wet. I could seal with 10 or 20:1 mineral spirits:silicone, but I'm too lazy for not enough gain.
I have a couple velcro strips to hold open door. When I don't seal these, water will leak through and drip onto whatever's below, so I seal thos spots.