I was the other way, I have a few hosts that I bought as pistols. The rest I had built from parts kits and barreled receivers. I have a case for foregrips and stocks. As you must know by now OP, you can't remove the trigger pack unless you remove the endcap/stock assembly. I have never found it that tough to store the stocks away from the receivers. Since I have almost 25 host guns/barreled receivers, I wouldn't want to spend over two grand in stamps. I would much rather buy ammo than give it to the Government. Of course buying a sear today at over $40,000, so another couple thousand in taxes might not bother them. It is not like I am worried that a Tac Team is watching my house or me at the range switching hosts.
Scott