If you buy more than 20 are there fixing on them?
Yes you can buy more than 20 grow bags. Just submit a request on our contact form with the details and we can give you custom order pricing: https://www.bootstrapfarmer.com/pages/contact-us
How do these bags hold up against gophers? Will they chew through the bottom?
Good question which im afraid I don't have a definitive answer. It takes a lot of effort to rip the fabric. I imagine a gopher would need to put some effort into it but it could get through.
These are made out of a leach free food safe polypropylene fabric woven plastic. A gopher could probably chew through but it would not enjoy doing so. We have never heard of anyone mention that they had a gopher chew through yet. If this was something you were really concerned about you could line the bottom with hardware cloth which is a steel mesh available at any hardware store.