In terms of powering things from a Leaf's DC CHAdeMO connector, you used to be able to buy Setec V2L 3kW and 6kW units from
www.evsiphon.com, but no longer. There is still information about V2H more broadly on that site, however. (And there might still be alternative sources for the Setec units.)
However, just in general you can connect a "12V" inverter to a Leaf just as you could to an ICE car; even better, since there won't be any exhaust emissions to deal with. (You can run it in a garage with the door closed!)
Perhaps connecting under the hood to the 12V system is what you mean by "being done, but possibly badly", but I think "badly" is overstating it. The biggest limitation is that you can only go so far in inverter wattage before exceeding the current budget for the Leaf's 12V charger. You won't be getting 3kW+ that way.
If by badly you just mean "home-brew" in the sense of cables everywhere and the solution not being "tidy", there's some assistance for that.
First, if you don't like using jumper-style cables to connect to the Leaf, there are cleaner wiring kits available here:
www.evextend.com
Second, if you'd like the inverter itself to be more packaged (and ideally weatherproof), there's this source:
www.cargenerator.com