I think i'll have to look into the truma heaters if it's right they dont need a hole cutting into the body - i want to do as little chopping as i can get away with
for the water storage tanks, i looked at the location (for mine its opposite the fuel tank) and i'll get the biggest i can fit in which will be around 70 litres i think.
for the waste tank i'll be fitting it behind the offside rear wheel and it will be alot smaller 45litres ish, if you do a lot of camping where you stay for a while on camp sites then you need a larger waste tank as it saves the hassle of moving the van to empty it, as you cant really dump it on your pitch, but if you move around a lot like i do then you can get away with a small tank, or if you do a lot of wild camping then you can drop it as you move around
what layout are you going for Dave
have you got any drawings plans