For those planning on using a LiFePO4 pack wrapped in duct tape off Ebay that comes from China, I recommend Ping. Li Ping sells a decent Ebike battery for the money with the best reviews. Everyone on www.endless-sphere.com
who is an Ebike geek, prefers his product and service, for the money. The other sellers are a toss up when it comes to quality and service. I only say this from what others have said after dealing with him, and with forum members not happy with the quality of other sellers. I have no personal experience with any of them, so take my opinion with a grain of salt.
Anyway, if your battery is one of those LifePO4 packs, it will easily fit into the Otivia box.
For example, a Ping 48v/20ah pack is about 6"x6.5"x11". It will fit quite nicely when mounted forward and centered in the box lengthwise, not sideways like mine (see Peugeot E-speriment thread)
Because the Otivia is so wide at about 13", you can easily mount your controller on one side, and your charger on the other side with tie-wraps, and still have a little room at the back for some spare tools/tubes, etc. This frees up your rack to be used for a good set of panniers if you wish.
This was one way I was going to configure my setup, until I decided to go with the Headway cylindrical cells to maximize room, and also battery performance.
If you are concerned about heat, I would simply recommend drilling some holes on the bottom of the box. Some on the front bottom, and some on the rear bottom. Also, a few in the center to prevent any rain from accumulating in the box.
The resulting air flow should be more than good enough to keep your controller and battery cool for day to day use, as long as you aren't running max speed/current all the time.
And of course, you can leave the lid open while charging, to keep the charger cool. It will definitely work, and it keeps everything tidy, safe when locked, and protected from the elements.
Also, if you do want to use an Otivia Box, I highly recommend you ditch the cheap plastic mounting brackets that come with it. I got a piece of 1/8" x 3" wide aluminum flat stock from the hardware store for about $7.00, which provides much more strength to hold onto such a heavy load. See my other thread showing how I did this.
The red lines on my drawing are basically an easy thin plywood box you can build to hold the battery stable, and strap the controller and charger to. Using thin birch plywood also allows you to easy drill holes to mount switches, run wires, and is still light and strong enough to keep things in order.