For a tent with a expensive SIG or ZIG it is always wise to use a footprint ground sheet,some tent makers make ones to fit specific tents and not all are made from strong puncture resistant,tear-proof material so you require to do you homework before you buy them.
Many campers recommend builders tarps for this job,But in my opinion and experience of builders tarps as groundsheets the are 100% inadequate.
The open weave is not designed to walk on and will puncture with the slightest stone or twig under the sheet. and once puntured will tear very easy. They will keep your SIG clean but will not keep it safe from damage.
Their is only one material for Footprint ground sheets I would recommend,I have tried and tested them for over Two years now with outstanding results.
These sheets are very strong and tear-proof you can cut them to any shape and size and will not fray, I will give you the link to the Flexi-liner,read what they say and and it is all true ,buy at the low price,as you will not get the insurance as you will not be using an underlay
http://www.pondkeeper.co.uk/pond-liners.asp
All the best
Rex.
