krylon's fine for what you're doing.
There's better stuff, but the prices are astronomical if you're just painting "cheapies". If you get a high end airsoft gun and want "real gun paint" there's some better options, but right now, that's just a waste of money.
I'd be using krylon on more things if they had a foliage green paint
If the sanding + krylon doesn't work, try using tesco model paint. It's specially formulated to stick to plastic, so you can go with that, plus it comes in camouflage colours. Any hoby shop should have it.