I did this about a week ago on my Innova Deluxe Bag and it turned out GREAT! I taped the perimeter of the bag about 1 in up and put 2 coats on the bottom, the 1 inch showing of the sides and the bottoms of the side pockets (since they are raised already I didn't go up the sides of them). I put a 3rd coat on the bottom only but I don't think I really needed it. I just figured I had it out so why not...
I used a foam brush that just fit in the can. Worked perfectly. If you do multiple coats over long periods of time (I let each coat dry 1.5 hours), wrap the brush in Saran Wrap to stop the plastic coating from drying and ruining your brush for the next coat.
Results are exactly as yours. 1st coat absorbed into the fabric. It looks kind of strange and you might question your decision at this stage but don't stop here... Second coat stayed above the fabric and forms the waterproof barrier. Third coat is just candy on the jelly roll on the cake.
Cost of Plasti Dip (Home Depot $2 cheaper than Lowes).........$6.99
Cost of foam Brush..............................................................69
Awesome implementation of awesome idea.......................Priceless
Sorry, haven't taken a picture yet, but thanks for the great idea.
Plasti Dip (don't let the yellow fool you, comes in black too):
Foam brush:
