I have bought 7 sets and fitted my 2nd last weekend.
They are cut larger than needed, to pattern, and are very easy to cut to shape with a Stanley knife.
I stick them to the underfelt using spray contact adhesive (Evo Stik)
If you take it slowly and carefully, you can make a decent job of fitting them, but don't forget the holes for the seat runners and the beat belt anchorages, before finally gluing. They are not easy to find afterwards.
If you have a later model with the box on the rear bulkhead, you may need to renew the hardboard panel if it is warped. I used 4.5mm ply, which is very easy to cut to shape with a jigsaw.
Let me know if you need more info.
Make sure you specify LHD or RHD when ordering, as the mats around the pedals are different.