is a long running thread with much good input.
My build has, unfortunately, stagnated due to matters outside of aeromodelling - yes, they exist! Nothing bad, but all too 'interesting' in many ways.
There is plenty on that thread about Sig's unfortunate choice of battery bay and hatch, including my topside hatch and more aft battery placement alternations. In a nutshell, to swap a battery that is in a tight spot between firewall and wing LE former, the model must be held upside down, then flipped over when the new battery is connected and the model's ready to power up. Not a lot of fun...
Even so, my 2650mA 3S will be an overyly tight fit. 2300mA/3S drop in nicely. Mine's getting an E FLite 15 and around a 10 x 7 or 11 x 7 - have a 'fitting' UC that will offer more ground clearance to the prop.