Welcome to the forum Keble6. Straight away I have to go with Max's first comment and I'd say an inflatable is the wrong boat for this use. I'd go for an alloy flat bottomed punt or jon boat style like this...
It only weigs 32kg so very easy to carry with a person each end and will easily skid up and down grassy banks, concrete steps etc far better than an inflatable with no puncture risk.
Car topping will be no problem and they can be stored tucked away so many places on the ground or hung on the outside of a garage etc.
Capacity for doing the sort of maintenance work you mention is excellent as the inside space is almost the same as the outside size unlike an inflatable where the tubes are so bulky.
It will also suit chucking tools down from the bank far more with zero puncture risk. Similarly if... as an example... you come across some brambles you want to cut back and take away an inflatable is totally unsuited.
It will also move through the water so much better than an inflatable with a very small or elec engine.
I've been knocking about the rivers on an off for 50+yrs and needing to do maintenance tasks that involve treating the boat as a waterborne wheelbarrow so the above advice is based on experience.
I think an alloy boat might be lighter but 20yrs ago the makers of this GRP punt (Granta Boats) were close to us and they were very popular workboats locally.