Gut feel is the a payload of 753kgs isn't enough for a 500 litre tank and a 2 man operation. Weight of water, tank, ladders, roofrack, diesel, 2 operators, 2 hose reels, battery and other kit will overload the van by far.
Both our single operator vans have 500 litre tanks and on some days they can each empty them.
Son and I worked for 4 hours each on Friday from my van and we used about 400 litres. We had to stop as we stucked the tank dry. Minimum would be something with a 900kg payload, but even that is questionable.
I have a Citroen Relay SWB payload of 1154kgs, 650 litre 2 man setup and that can be a bit small for the stuff we carry around - 2 hose reels, a variety of poles, backpack and additional 20l filling plastic container.
Personally, I won't consider anything less than a SWB T280 Transit, Relay, Boxer, Ducato type of van. Son in Law has a LWB Hi Roof Transit Connect and I personally would say a Connect T230 would be too small for a 650 litre tank, hose reels etc.
Spruce