The weight of seam sealing really depends on how thick you apply it, but generally it would be about 0.5oz and not likely more than 1oz.
Some seam sealants are quite thick, so users will apply them quick thick but they still don't work very well if they are thick like glue because they aren't soaking into the material to seal right down to the internal plastic layer. It's lighter and better to dilute the seam sealant a bit (if you have a thick one) so it is thinner and can be painted on easily where it soaks in. I've done that with another pack that I owned made of the same material, and it added about 0.5oz.
The company "Gear Aid" (formerly McNett) makes a variety of products that can be used, and often these just vary in how thick they are. I think "Tent Sure", "Seam Grip" and their shoe repair product are all basically the same thing but in different thicknesses. So if you buy the thinner option (Tent Sure) then you shouldn't need to dilute it and could just paint it on.
Sealing the seams on the inside looks nicer but a few of the seams (near the frame) are hard to access from inside so you'd likely need to seal those on the outside.