The hardest part of the job is geting the listing lines hog ringed in place to the springs. Be carefull when you remove the old covers to notice how they were installed. Take notice of where the front edge of the cover is with relation to the front edge of the spring assy. When you start installation, the cover will be inside out so you can get at the reinforcements of the listing lines. The listing lines are the edges of the pleated section of the cover. These have to be secured to the spring or the cover will move around and look crappie. The seatcovers usually don't have metal or plastic rods in the reinforcements like the factory ones do so save them from your old covers or you can use 3/32' welding rod. To make this part of the job easier I use long zip ties around the listing line reinforcements of the cover and around the listing line part of the spring. This way you can snug them down a little at a time but leave them a little loose. This way when you turn the cover right side out and install the plastic lip under the seat frame. then pull the cover toward the back where it hog rings to the frame. With the cover in place you can then pull the zip ties tight and hog ring the listing lines togther.
Changing the foam makes it a little more dificult as the foam is new and thicker than used stuff. You will have to pull a lot harder.
The back of the seat is some what easier as the listing line is a "u" shape, so you can tell where it locates.
With all that said, it isn't that bad of a job, even for a beginer. If you not happy with the results just cut the hog rings remove the cover and start over.
The baby powder trick sounds good, I like to use dry cleaner plastic bags. Put the bag over the form so the cover can slide over it, this will make pulling easier.
Good luck:
Sam