Use this 2" heavy duty plastic dome with 10" x 20" trays. It will help retain moisture and heat to improve seedling germination. Includes 3 vents to help control heat and humidity. 

• Heavy-duty 2 inch tall plastic humidity dome
• Fits on most standard 10-inch by 20-inch trays
• Helps retain moisture and heat to improve germination success of seedlings
• Exclusive patented 3-way adjustable ventilation design
• One vent on top and one on each end for perfect humidity control