Experimenting with Gouache

This is done in mostly gouache, and a small bit of acrylic. I haven't used gouache extensively before, but having read a lot of artists/cartoonists I admire (eg.Voutch and Arthur Szyk) frequently use gouache, I thought I'd give it a try. I've always been fearful of gouache, for one, I was told once that cockroaches love to eat it and subsequently destroy artwork, and secondly it's also a fairly fragile medium, because as soon as it comes in contact with water the gouache reactivates and bleeds. This suggests to me that it's archival quality is poor, but I'm probably wrong because Szyk's work dates back a while and it's surviving. So, I'd like to throw a question out to anyone who's experienced in gouache: What would you recommend as a sealant/fixative or varnish that works effectively with gouache?

Despite these minor drawbacks, it seems the pros outweigh the cons, as I found gouache a pleasure to use and I'm very pleased with the results. It's the next best thing to painting in oils, but minus the fumes, which is great. It's other downside is it dries quickly, but I coped.

I'm pretty sure I'll use gouache for whatever book I illustrate next...