They use Wydale tanks because they are cheap as chips,they are just storage tanks not supposed to be used to carry liquid in.
That one I told you about his name is Neil he will not put a tank in you’re van that is to big for it,he can supply everything you’ll need for window cleaning,you could have a flat tank with pump the lot all built into it if you put a sheet of ply over the top you wouldn’t even know you had anything in the van.
I wouldn’t go for an upright next time I don’t think unless it compromises having a heater fitted,if you have a tank frame of sorts it makes it easier to bolt the heater to it 1 or 2 man heater that is
The single user heater is very heavy although in pictures it may not look it,it’s very heavy.
Not cheap those tanks he makes but like most things you pay more for they are better mines 7-8 years old never leaked at all I had the tanks you mentioned and they leaked like a roof with no tiles,if he makes you one get him to cut a 6” hole where you want the lid because the lid did go on me from sticking the transfer hose in it for years so it popped off.
The lids Grippa sell are the best lids you’ll get.