I've been using a box trailer system for a year now and found it has served me well.I mainly clean domestics.Sometimes though its a pain in the butt.
Positives are:
My work vehicle is not a van but a 4x4
I fill the 400L tank on the trailer straight from the merlin RO and still be able to pop out in the vehicle whilst filling.
Lower maintanance costs than a van,road tax etc.
If work car is broken, can still use familly car with trailer.
Negatives are:
Having to hitch & unhitch the thing.
Manouverability.
Slow.
Having not really towed a trailer before this is a skill I'm still getting used to. Some houses can be difficult to access with a trailer.Also parking close to client can be obstructed by other vehicles.I got myself a Freedom Trolley which fits nicely in the trailer
& helps with most of those jobs.
I got my 'Domi' system from Stuart at Skypole.There are others about-try Stream.
My box trailer is looking a bit battered already-tail light fins and mud guards all bent but all in all I thought it a cheaper option than having to spend on a reliable van and then have it fitted out and then have the van replaced a couple of years down the ine.
Hope that helps,
Filllllll