Passively heated green house

I have been trying to grow tomatoes at my home near the coast for 30 years without much success. My plan is to make a small greenhouse 8×12 ft,  which will be passively heated to keep the night time temperatures above 60 degrees  in the summer. I have gathered some cast off materials and have just started construction. I plan to ventilate to avoid overtemping in the day time using a household fan with louvered door and an automatic temperature sensor, (Bayite-TCF-3A017) from ebay at $13. In order to design the quantity of the heat sink, I will be starting with a weather station for the temperature monitoring.

https://www.amazon.com/Ambient-Weather-Wireless-Internet-Monitoring/dp/B077Y765R4

This was $39. Needless to say I am on a tight budget. I will be posting all  of the temperature data in case anyone is interested.

My plan is to have the base line heat sink be a cement walkway of 2ft by 8ft by 6inches down the middle in a dark color. 55 gal plastic barrel of water in the corner, and then stack cement blocks filled with decomposed granite on the back wall as needed. I will asses the night time temps and add more heat sink mass as needed. My hope is to tune it till I get perfect temperatures without using much ventilation. I have lots of ideas about how to add additional heat sink if needed.

I would love to hear about others who have already done this, and may give me some help. This is my very first effort.