[skyking]

the front vent cover only serves to allow the vent to be open in all conditions. If you simply remove that cover and build a very simple fairing behind it, no need to delete.
Same with the roof air. if it is not needed/not functional, it is easy to replace with another low fan cover. A small fairing behind each of those will re-attach flow nicely.
The roof air is typically installed through a standardized 14" by 14" hole.
I picked up a replacement fantastic fan for my bathroom for $126 at PPL motorhomes.
The better unit is about 160, with a thermostatically controlled fan.
I have one of those at the back of our trailer and it is very nice to turn on the fan, set the thermostat and go out for the day.
As the temperatures go up, it only runs as needed to keep things reasonable.