Seam sealing silnylon?

Tape that works on silnylon is rare and expensive

Use silicone caulk diluted with mineral spirits 1:5 or so – that's what I use because I happen to have those already

Or McNett Silnet

Or Permatex Flowable Sealant – I think that's probably the most recommended here. Intended application is sealing automobile windshields

Set up tarp so it's stretched. Apply to outside. Some people wipe off excess to make it less visible.

Perfect, thanks a bunch!

Edit 1:5…. 1 caulk to 5 mineral spirits?

I might try that, I have both.

yeah 1 part caulk, 5 parts mineral spirits

you could try a small spot, let it cure (for a couple days), make sure it sets up good and looks like you want

oh, it takes a while for the caulk to disolve, like 10 minutes. Stir it occasionally. It should form a uniform goo.

there are probably 50 threads like this with slightly different directions

If it takes you 10 minutes you are doing it wrong.
A minute will do it :
https://www.youtube.com/watch?v=0tCyT9p8Uys&list=UU0PuLUKvG7Fxxex5BMVK4vw

In the original version of my "sealing the Moment" You Tube clip you could see me doing the 1 oz or so that I needed for that tent in about 30 seconds.
I then edited out some of that just to have a shorter clip but generally (if I am not talking on camera) it does take me less than a minute.
But I have had some practice.
What I mean to explain here is that it is rather simple and quick to do unless one particularly wants to make it more complex than it can be.

It took you maybe 2 minutes

Nice video

I put more mineral spirits which maybe makes it take longer? I'll have to try a smaller amount next time.

Regardless, no big deal, I just let it sit there a couple minutes, then stir it a bit,repeat…