I have a 2006 Colorado 600 DLX. We have not slept in it yet. However, I've put it up twice and it seems pretty good (well, for what I paid for it, being last year's model). I don't think the riser is a SIG. Only the pods have a SIG. I had a look on the Vango website and I think the riser has flaps on it that you fold up against the flysheet.
But I could be wrong... :)
Whatever, Vango tents are very good quality, have a lifetime guarantee, and a long, distinguished pedigree. That is what swung it for me in the end. I was comparing the 600DLX at £124.99 against a Eurohike (Swale, I think) for the same money. No contest.
What you need to do is look at one fully erected, go inside, see if you like the space it offers. So look out for a tent show, or make a trip to a big retailer. If they have Vangos, you'll be able to answer your question about the groundsheet. And remember, always buy quality. Don't take a chance on something crappy, or you'll pay for it in the long run.
We have the vango colorado 800dlx - not had chance to try it yet, but I have looked at the pitching video (several times)and read up on it and the riser groundsheet is not a SIG. Its basically the groundsheet with sides that hook onto the side of the tent.
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