Where are you based?The easiest way is to use the trolley in the van and run a hose from the van via the trolley.Tank, Trolley, reel, pole. You can either submerge the hose into the tank or connect to the pump on the trolley direct.
When had a trolley, I made a simple wooden ramp that fitted inside the van. Stop. Take out ramp and set it on rear of cargo floor. Roll trolley down ramp.Reverse proceedure to get it back in.Old gits like me can't be doing with all this heaving and straining, might do some serious damage
Don't go to the expense of tanks just buy these 2 whale pumps and use them together as a transfer pump with a 12 backpack battery or run them of you car/van battery. They will transfer 25/30 liters per minute with.Fill you trolly from you barrels or empty trolly into barrels.I used them for 3 years.Workrd very well.I still use my 2 for transferring from one butt to the other, they are small but do a very good job.I tied them in tandem so they will go onto a barrel.
Call me if you need to speak to someone or visit a local gym who is helpful.