This had a 400 litre upright tank fitted in. It only just fit, i doubt you'd get a 500 litre upright in it. I don't think a layflat would be an option as you'd struggle to get the hose reel in. It needed a boot protector due to trapsing hoses, i suppose a bumper port could of been fitted but we didn't want to drill the bodywork on it.
that looks lovelywhere do you put your poles?