Guessing you don’t do any pressure washing or softwashing Adam?
I love a truck, but I couldn’t use one simply because they don’t have the same practically as a van.
Enjoy it, although I can’t help but think you’ll want a van again in a couple of years 
No I've done it all carpets, softwashing, gutters, pressure washing etc and now just stick to windows. I don't have the time to do anything else and it's all too much faff.
I looked into one years ago it wasn’t practical once you put a tank in em there’s no room left,the only option would have been a bespoke tank that had pump and DI built into it. No room for poles and no room for a diesel heater.
Dont need any room left. All I need is a tank, pole, battery, controller, pump and maybe a backpack.. I don't carry a d. I or r.o I have a static system. both my 25ft and 39ft poles fit in fine. Don't need a diesel heater, will probably fit an immersion.
I did question whether it was big enough but its perfectly fine if you just clean windows.
Wouldn't fancy 500 litres ratchet strapped personally.
If you have heavy enough ratchet straps the weakest point will be the anchors. The anchor points on this truck are probably better than what most have drilled through their van floor with a cage and certainly better than flimsy van anchor rings.
The thing is adam is using it as a dual purpose vehicle....work and leisure......so it's more suited for that....
from my experience its always a bad idea to just have one vehicle for both....its just a big faff taking your wfp equipment in and out all the time.....
A dedicated work van and a separate car for leisure is the way to go ideally......its also easier for business expense purposes....
I would agree with you, if you make use the car.. . I had a van and a car and hardly ever had a need to use the car because my girlfriend has one so we just used hers. I just got fed up of it sat their doing nowt and paying 2 lots of insurance and tax.
I could have just kept the van only and managed but to be honest I just wanted a truck. I go fishing quite a lot and would be ideal to take down some of the farm tracks and i fancy doing some green laning.
I just wanted one, a new van didn't do anything for me.
Not sure how having 2 vehicles is easier for expense purposes though...
He could always buy a small box trailer for items he doesn't use when window cleaning and tow the trailer to booked in jobs that way he doesn't have to keep putting stuff in and taking things out of pick up
To be fair there's enough room to fit a gutter vac and poles of I went for a custom tank and like you say a pressure washer could be put on a trailer. Not that I'm interested in either at the moment.