Tank,
1" outlet,
filter (optional),
some sort of on off valve to isolate tank when trolley removed,
male hozelock (or eqivelent),
change the end of the hose that presently goes into the barrells to a "stop female hozelock" ( or equivelent),
Hozereel of your choice with pipe and fittings to connect the reel to the trolley,
And thats about it really, not forgetting protectakote for the floor and some sort of fitting arrangement for the tank. Cheers Nick