That`s the frost stat option that comes with the unit as an option,i will say that the unit does need to have 2 runners made for the unit to stand on and then be bolted through the floor.The place who are doing mine i know them and they made up 1 for each end for it to stand on,if you bolt it straight to the floor it won`t be level as van floors have ridges on them.It will take them longer than they first think aswell,so far they have given it 4 hours and will need another 2 on wednesday.It`s not just a case of bolting it in and away you go you have to plan where holes can be drilled as each van is different.
Thats it make sure its fitted properly.
Hoses that go through the floor should also have a metal flange round them, and the exhust should go out to the drivers side, better to the rear. I had a new set up so mine is fitted into a cage that i had made bolted to my skid tank.
You can get some good info about webasto from diesco in Ipswich.
There are lots of options, i went for the bigger KW heater as i run 2 hoses from it. I also had a timer fitted, but if you have a frost protection on it, then you probably wont need it.