I've not heard of lacquer, but I have heard of resin. I'm pretty sure regular fiberglass resin is fine so long as you use hardener. It works the same way. I bought a can at Walmart, a decent amount cheaper than auto parts stores.
Generally, people use fiberglass resin (also called polyester resin). However, there are others who you epoxy resin to harden parts as well. The difference being that epoxy resin, while still horrible for your health, is slightly less horrible for your health than fiberglass resin. It also doesn't fume nearly as much as polyester resin does.
I have recently started pepakura helmets/ props. I have found that fiberglass resin works great. Only 5 ounces of fiberglass resin will be enough to coat an entire helmet, so I would recommend purchasing a 30 oz container ($20). A container that size would be great for probably 2 whole helmets if you use rondo.
You apply the resin to the bare paper/card stock helmet to harden it for later 'shaping' applications (such as Bondo).
If you do plan on using fibreglass resin, ensure to properly research the application process, as well as the safety concerns as the stuff can be quite toxic. Don't let the toxicity put you off, though. An open outside space along with a respirator will do just fine.
Yes, it is used for this purpose. Painting it on will basically turn it from paper to plastic and then you can do even more with it. Check out these videos by Cereal Killer, it will teach you about resining first and then show you how to use it. http://www.405th.com/showthread.php?t=36689 Just start watching those videos in order and you will get the idea. Reading and watching... Welcome to the 405th! oh yeah and building
Polyester (fiberglass) resin is less expensive but more toxic (wear a respirator) and shrinks as it cures (affecting your part sizing). Epoxy resin is a little more expensive but not as toxic, doesn't shrink, and is stronger than polyester resin. Either can be used with fiberglass mat/cloth for strengthening a hardened piece. People have also had success with using thinned wood glue to harden their parts, which is not toxic at all but not as strong as resin. The main thing you'll want to avoid is getting the paper too wet and it deforming during the hardening process. Don't harden the entire model in one go, and if a model includes supports, use them. There are a number of introductory threads on the forum and you really do need to invest some time in reading them for gaining a rudimentary understanding of the process. There are also some great videos out there, such as Cereal Kill3r's and BenStreeper's, plus many more on YouTube. Welcome to the asylum. :lol