Yes, I have, and yes, it can help. On my coach I have done it both ways, I have a thermostatically controlled fan at the inlet connected to the 12V DC power, as well as a solar powered exhaust fan mounted at the roof top vent. I went a bit fancier on the lower fan as it is a PWM dustproof 120 mm computer fan, connected to a temperature sensor with variable speed output (about $8 on ebay shipped from china,
https://www.ebay.com/itm/PWM-4-Wires...S/312613052371 ), meaning the hotter it is the faster the fan blows (and the louder it is). The roof mounted exhaust fan is not nearly so fancy, it is 130 mm Rosewill SEAL IP 56 dust proof computer fan (non PWM version) connected directly to a small cheap 4 watt solar panel. This provides enough voltage to spin the fan at some rate in any bright daylight condition. Total cost was under $20 buying the solar panel on close out, most of the cost was in dustproof fan.
p.s. the exhaust fan works better for removing heat from the area as the inlet fan is more prone to just recirculating air inside the enclosure.