You still have annual van costs: insurance, tax, mot, service, plus cost of buying new van when needed.
Also running the RO system, making sure to protect it from frost damage in winter etc.
Added to that in future there will be Making Tax Digital to deal with.
So yes, earning £500 a week for two short days sounds good, but it is not £500 profit. The less you turn over, the higher the proportionate costs of your overheads.
I beg to differ. My van is 13 years old on 85,000 miles from new and barring (another) prang or catastrophic failure it will last another 5 years. I could put a trailer behind my car rather than get another van - especially when my turnover drops below £2000 - but I won't as long as my van lasts.
Sure I'll get my oil and oil filter changed annually but why replace air and pollen filters if your mileage is less.
Less miles means less work for an MOT pass. Less wear on tyres and brakes.
My extremes used to get replaced every two years - now I get four.
RO lasts longer as less water used; same with resin and filters and if on a water meter.
The only constants are road tax, mot and insurance at about £1000 a year total. And if I stopped completely we would probably run two cars instead of a van and a car.
Not knocking on the door of higher rate tax mean earnings do not get taxed above 20%.
£500 a week is £26,000 turnover. Not to be sneezed at from two shorter days. Especially if it is cream low mileage work.
Making tax digital isn't necessary if turnover below £50k then £30k and only a few hundred to set up if that.