Elise camping is great, good car to drive, minimal room to take unecessary things . . . we have done lots of long trips to europe and pack things thus :-
waterproof jackets : in a stuff sack next to the heater/battery (this is an S1 - you may not be able to do this in an S2)
tent and 2 x thermarests (inflatable sleeping mats) : behind the seats
clothes : in stuff sacks which double as pillows down the side of the seats / behind the drivers seat
sleeping bag, water : pax footwell
sleeping bag, camera stuff, cooking stuff, roof, everything else, boot
This gives loads of room in the boot to get the roof in and out quickly and some extra space to carry food/wine, etc as necessary
The tent we use is smallish . . . we bought it mainly for travelling in the car and travelling by foot/plane, etc so it's specifically small and light . . . and very stormproof (camping in the mountains in the US/Canada we have had very bad weather before and the extra expense was well justified

and I've seen friends tents blown way in Scotland before) . . . we also use down sleeping bags as they pack down to about 1/4 the size of an equivalently warm man made fibre filled one, about the size of a bag of sugar, and still keep you warm even when it's freezing outside (we camped at the first Doune this year and the tent/cars were frozen solid over night) . . . again useful if you are travelling with a rucksack, or an elise . . .
For us we could travel indefinately in the Elise with the kit we can carry if we had the time to do so
Fd