I think all the internal ventilation is, is to disburse heat and not flue burnt gasses as you say the external flue vent MUST be fitted.
I bought a c/van with a double internal vent the extra was added for better venting in hot weather so as long as the gas vent is fitted correctly you shouldn't have a problem. To be sure contact electrolux leasure equipment department and ask them.
bb
January 2011