My son and I are in the process of finishing our nets we built with the help of member of our fishing club(GBF). Spare varnish is the way to go and make sure it's marine grade. You can opt for spraying it on which requires 6 coats or brushing it on which requires 3 coats. You can sand between coats with 220 and 400 on you final coat. We opted to brush and are finding it takes a long time to dry between coats and runs pretty easily. Still waiting for our first coat to dry as it have been cool and humid here lately. Standard bags are available for $10 or less but the Ghost bags are about $21-25 depending on the size. I ordered a ghost bag from Fishwest as they have free shipping. The varnish runs about $15 for a small can. Be careful or your free net is going to cost you $30-50 to re-finish.

Good Luck,

Jet