ready to roll icing - does it crack/dry out?

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I have never used ready to roll icing before, and am planning to cover a cake and make some simple shapes. It's that supercook stuff that comes in a block.
Does it dry out and crack? If so, what can I do to stop it?
Just did a little trial shape last night and it seemed to crack a bit. I'm colouring it too, so it will have been kneaded a bit.
Any tips?
Also, I know you need to put something under it - is jam the only thing you can use? And does it really need to be cooled boiled jam??

You need to knead it til it is warm and supple

Also roll out on greaseproof paper as then you can pick it up and plonk over the cake

last time I used it I just used raspberry jam it was fine

(my latest effort on my profile!)

I've not used the Supercook roll out icing but I've used ones from a cake decorating supplies shop and they've been fine. They come in a big range of colours so you don't have to faff around kneeding in colour (although I did mix some powder colouring into small amounts of icing for some intense colours I needed for the small decorations and it was fine)

When it starts to dry out ie. after its been on the cake for a while it just tends to go a bit harder and drier on the outside but not actually crack. However, like I said, it wasn't the Supercook one

no I have not used supercook either I have to say

Actually I'm talking rubbish - it's not supercook, it's DR Oetker (sp??).
Will give it a go anyway.

Dr O (German firm) bought out Supercook earlier this year - all their stuff is gradually being repackaged. And thank God they've finally cut out the hydrogenated fat in their ready made icing!

I used to use ready to roll icing and never got it quite right.
This year I found a READY ROLLED icing that comes flat in a huge circle, but wrapped round a tube, just unroll it over your cake! Fab!
And I'm not usually one for labour saving devices but for the extra £1 instead of all that effort....