Jury Rigging Radiator Expansion Tank

[Carrameow]

To my best knowledge the hose on my 83 240D Radiator is open ended. I'm a little nervous about radiator Boil Over some hot day when I'm cruising down a NE Freeway at 100 degrees F with the AC on so I was thinking about getting a Plastic Expansion reservoir and sticking it on the end of the hose as a Summer Precaution. Is this a bad idea? Truthfully I dont like modifying the stock condition of my car--I didnt even change the radio or put on Fog lights because of this feeling.