I have used the smaller gripper-type box mods like the Segelei/Ovale V8 and Smoktech VV Gripper at indoor concerts stealth
vaping. I'm not aware of anyone currently selling the Ovale V8, but keep an eye out at Discount Vapors. $30. Neat little
mod with a better build than the Gripper. DV offers a neat leather pouch/lanyard especially designed for it that works great.
Not out on the market yet, but by next month the Segelei Tmax is a VV/VW box
mod with a durable metal body that will use an 18650 battery. Below pic shows the prototype and the larger one that will be for sale. Not sure who will be selling it first.
The Smoktech VV Gripper was a great idea in form and performance, but suffers from build quality. For the price though it might still be a fit for you. Mad Vapes and Got Vapes has them for around $30.
Segelei/Ovale V8
Segelei Tmax
Smoktech VV Gripper