REI carries a good line of seam sealer. There are several choices and ways to apply it to seams. Some use the seam tape which is supposed to work better but take a little more effort to apply and others use the brush on stuff.
Ive used the product "Seam Grip" extensively and it works well as a seam sealer. And just as importantly it is a miracle for in the field repairs of rips, tears, and punctures for most any matierial. I always have a little tube of it on hand for patching up down coats, tears in the tents fly, pin holes in the sleeping mat, rain jacket snags ect ect.
i just did the silnet and mineral spirits....did my SL3 in like 15 to 20 min. It was slow going at first because I don't think I added enough mineral spirits and that silnet stuff is really gooey and doesnt spread, but once i got the right mixture it went quick.....silnet is like $6 and a $7 thing of mineral spirits from home depot and you should be good go