It's a good idea to spray a gloss clear coat over the decals. It will give the model a nice gloss appearance as well as preserving the decals. My advice is, don't use TS-13. Because it's a lacquer based paint, it can have some bad effects on decals. I've used it a few times and it has screwed a few of my decals. And they were Tamiya decals.
It can be used, just make sure you put it on in very thin coats. It's when you put thick coats straight over the decals that you'll have problems. Do about 3 or 4 thin (mist) coats, then you can start putting on wet coats. The thin coats will hopefully provide a barrier between the wet coats and the decals. And make sure you let your decals dry atleast overnight before spraying anything.
hope this helps.