I'm a Skinning(300) Engineer(301).
I find that the Skinning hardly makes any money at all, and that Engineering is far more lucrative.
The bottom appears to have dropped out of the Skinning Market for everything other than Rugged Leather. ALL my leather goes to my Guild - It's not worth the hassle of trying to sell it, and I receive other favours in exchange for Leather - Pots, Reagents, Good Karma. By Contrast Engineering is turning into a little Goldmine though.
There are several quests that require high lvl engineered goods: Gyrochronatoms, Mithril Casing, Unstable Triggers, Hi Explosive Bombs, Delicate Arcanite Converters. Research these quests and put just the required number of items into the stack. Post them on AH and run a quick advert.
The profit made over a good *Casual* week will surprise and entertain.
No profession is designed to make money exclusively over all others. The money is made when 3 or 4 high-ish tradeskills work co-operatively , trading goods/reagents between each other to made things for the lowest cost to them, for their own chars and alts and to sell for a reasonable price (to others) rather than for the highest possible price.
My Advice is continue with Engineering, maybe dropping skinning for mining for the convenience, and hook up with an Alchemist (ideally one who is also a Herbalist).