2004.5 Dodge Ram 2500 SLT 4x4 Quad Cab.

Best Buy lists the rear door speakers as 5.25 inch. Crutchfield list them as 6.5 inch.

I removed the speakers and the hole measures 5 inches. I bought some 5.25 inch speakers and when I went to install them there was about a 1/8 inch air gap around the outside of the speaker. Tomorrow I'm going to buy some 1/8 hardboard and make a ring to put behind the speaker.

Should I put any kind of sealer behind the ring (between the back of the ring and the sheet metal of the door)?

 

Nah. If you want, maybe a little RTV gasket maker but I wouldn't worry about it to much.