DIY 12" Dayton MKIII sub box

[MTKAN]

Hello, first time poster. I have jumped into DIY because of forums like this one. It inspired me to try my hand at speaker building and hence my efforts at building a set of Harvey FR speakers. I like many of the qualities of the Harvey's but feel that they lack in the bass area. With that in mind I ordered a Dayton 10" MKIII to fill in the bottom end. PE sent me the kit, but sent the 10" box and the 12" speaker and 500 watt amp. Now my dilemma. I will later build a 10" sub with the box I have from PE for my Harvey's, but want to use the 12" and and amp to replace my HT sub in another system I already have. What would be a good size box to build to utilize the qualities of the 12" MKIII? I would like to stick to a sealed box for simplicity. Size or/and shape will not mater. My HT is in a room approximately 12' x 22' x 8'. Use will be 75% HT and 25% music as I have another system strictly for music. Sorry if I have given to much unnecessary info or not enough. Thanks in advance in helping me sort through all of this as I am very new to all of this.