thick ground sheet would be good. Bear in mind that the size of the tent as specified by the manufacturer is for people sleeping in expedition style - essentially like sardines in a fan shape - so you may wish to get something larger. By the way if you went with a RTT solution then you can buy an enclosed room underneath - this you can cook in (be sensible re fumes etc). Some friends of ours also vented their Webasto in. However, the under-room will only really seat 2 + stove, 4 at an absolute push. The larger tentipis will accommodate 6 or 8 seated, put all your gear around the outside. You may also want to consider tent pegs. Tentipi ones are rubbish lightweight alloy and in Iceland you will likely have a mix of hard rock and ash - so I suggest that you get some proper rock pegs and some sand pegs in case you get to some ash. Packing sleeping bags - yes a pain, but so too will be your air mattress or camp roll. We leave our bags loose in the back to air (even though you can leave them in most RTTs). Out in the highlands there is little shelter so putting your truck on the windward side is a good thing. Some campsites have purpose made banks to provide wind shelter for ground tents