There are a few different ways to do this.

One is to package /Users/username/Library/Preferences/com.apple.dock.plist and distribute that as a package with the Fill User Template setting checked (so that new users get the dock setting when they log into the machine the first time) and, optionally, the Fill Existing Users setting checked (so existing users get the dock settings, although this will overwrite any existing dock). This is most useful for freshly-imaged machines.

Another way is to use a policy to distribute Dock items to computers, with the policy set to Once per user per computer. You won't have a lot of control over the order of the items, though. Items are added to the beginning or the end of the dock, possibly in alphabetical order.

If you want precise control, you might want to look at dockutil, available on GitHub. There's a bit of a learning curve, though.

Use a configuration profile. Or use dockutil.

Don't modify the user template for a dock setup - thats bad ju ju.

Dockutil as part of a login script is the best way. You can have it run once per user, or ongoing should you want to enforce the dock setting everytime.

Thanks all for the responses, very helpful.
I'm going to give the Dockutil a go and see how I get on.