Your technique is good, but why would you think you need a top coat of Krylon? If the PlastiKote doesn't bond properly you'll just be poapering over the cracks.
As far as PlastiKote goes it's fine, I would suggest you use the Matt Super range http://www.plasti-kote.co.uk/Product/pcode---4181/pccode---6751
Krylon has the advantage of coming in camo style colours in their Fusion range which incorporates an adhesion promoter for use on plastics. Socom Tactical ell it for £7 a can so God knows why you'd be paying £15 a pop.
PlastiKote is made by Valspar who have UK production and far wider distribution, Krylon is made by Sherwin Williams who don't. Hence the price difference.