i bought a nemo 3 months ago as my first van. i currently have a trolley system and when the van is carrying that and 100-150 litres of water with ladders etc, i get 55-60 mpg and thats mostly city driving. The payload is about 650 so i think you couldnt really have a tank larger than 250. Space wise its a bit two small if theres two of you but its perfect for one- the passenger seat folds into the floor so theres loads of space for step ladders or long poles etc. As i say ive only had it 3 months but theres been no problems and all seems pretty reliable so far.
however, two problems ive had with my model (1.3 lx). The fact its called a nemo means that last week some sod wrote 'finding' in front of it in marker pen. All sorted with some t cut.
the second problem was with insurance. The major insurance groups like churchill and even the compare websites have the info incorrect on the van. Basically, they all have it registered as a 1.4 when its actually 1.3. I have spent hours on the phone to various insurers, the DVLA and citroen and no one has managed to sort it, meaning i had to go to a broker to manually type it in. I dont know whether the problem was just with my reg or what.
anyway, aside from that I am extremely happy with the van, but as I say, its the only van ive ever known.
p.s due to size its excellent for parking, oh and road tax is 130 for 1 year.
let me know if you have any other questions