Tent seams

Are you using silnylon? Then you want to use silicone based sealant. McNett has a product. Or Permatex Flowable Sealant, Or silicone caulk thinned with mineral spirits maybe 5 or 10 : 1. Look at the label and make sure it says silicone

Or urethane? Then McNett Seam grip. Make sure label says polyurethane. After it's cured, don't let the stuff touch itself or you'll have a mess. Spread some powder over the surface. Talc works. I take wall board, scrape some off with knife creating powder, and spread it on surface. You don't want scented stuff, and I don't think corn startch works so good.

Or taped cuben? nothing

Actually, if your seams are fairly steep, you don't need to seal them. I never seal my seams and have never noticed any leakage. If the seam was on a flat section, then maybe seal it. But, most people seal there seams anyway which doesn't hurt – slight extra weight and extra time to seal it and wait for it to cure.