That would depend on who you ask. I don't think it's hard, but then again I've covered lots of models. It's like everything else you would do in the hobby, the more you practice the better you get.

RCU member MinnFlyer has done some great how-to articles and videos on covering. check them out as they will go a long way to getting you started.
[link=http://www.rcuniverse.com/magazine/article_display.cfm?article_id=67]Minnflyer Covering how-to[/link]
[link=http:////67.18.81.100/rcuvideos/magazine/reviews/352/cov1.wmv]Minnflyer Covering video, part 1[/link]
[link=http://67.18.81.100/rcuvideos/magazine/reviews/352/cov2.wmv]Minnflyer Covering video. part 2[/link]
[link=http://67.18.81.100/rcuvideos/magazine/reviews/352/cov3.wmv]Minnflyer Covering video, part 3[/link]

I hope this helps

Ken