Trick is to keep the iron on low and if you're having trouble getting it to stick mist on some 3m77. You can't cover compound curves as nicely as you can on a balsa or composite build, but if you plan ahead and use relief cuts you can go around most areas. I tend to do a strip along a joint/fillet and then use large pieces for everything else.
All of these models were/are covered with low tempcovering. The big jet was glassed first, but the others are done right on the foam. There are imperfections, but overall they look pretty good.