Cooling question.

[WallaceMFG]

Yes, close out panels can help with cooling. They reduce the chance of hot air being recirculated back through the radiator. There is a reason the OEM manufacturers have all that ducting in place on modern cars. The more cool air the radiator can flow the better it works compared to recirculating hot air from under the hood.

And for a fan to work at it's best the radiator should be fully shrouded. That forces the fan to pull air through the core, not in from the sides. Remember air follows the path of least resistance. As mentioned above, be sure to put flapper valves or turn the fan off at high speeds to ensure you are not blocking flow on the highway.