Hi Jim
I have been putting together the E-power system for Brodak.  Its funnly you mentioned the Fox 15 and the "10" sized system, that was the target.  The 10 system turns a APC 7x5 at roughly 14,500 RPM - that would be a very good Fox 15x!  

The 10 system was aimed at the 1/2A Pathfinder, which is the same size as a lot of traditional 15 sized airplanes like the Midwest Magician 15 and the Sig Akromaster.  I was a little concerned that folks running 15 system would wlso want ot use larger (8") props, so we brought out a new "15" system.  The 10 and the 15 sized systems are the same except for the battery; the 10 system uses a 3Sx1300 (103g) pack and the 15 uses a 3Sx1800 (133g)  roughly 1 oz heaver.  For that extra ounce gives you more battery reserve on a 8" prop size.

I do not recall - what size are the Midwest 15 profiles - 33" span and 250 square inches?  I just completed a Brodak Junior Flite Streak (31" span, 230 sq in), The only mod was to build a battery pocket in the wing., there was a lot of room.  Uses the  15 size system and the RTF weight is 14.8 oz.  Yeah I am psyched about it, out to go like... heck and really dance!  Gonna try it first with the 7x5 which can be purchased as a pusher, then will try the 8x4 and 8x6 to get the best combination of speed and manuverability.  Might also try it with the 3Sx1300 just to take another oz off it!

Also copied a couple pix of my brother's Sig Akromaster (34" span, 250 sq in) conversion from a gas model.  The Akro uses the 3Sx1300 pack and has a lot more room on the fuselage than the Streak; that was important because he did not have the option of slipping the battery into the wing (there is room tho)  The Akro conversion finished at 18 oz and it flies great.

The MW 109 probably has room on the fuselage for the battery, but I think I would opt for the wing pocket.  It also gives you the chance to slide the battery fore/aft (into & out of the pocket) for balance; just strap the exposed park of the pack to the side of the fuselage...

I do recall that the MW Profiles had a tendency to build heavy - if you can keep the weight under 20 oz you should be in great shape.  

Hey Jim
Your recollection of running Fox 15's with 7x4 or 7x6 props jibes with my own.  That is why I was so happy to get that match on the 7x5 APC.

If you go to the Brodak site there is (LH side of page) a menu item caled "ELECTRIC INFORMATION" click on that then click on the first item listed, Arrowind Power Systems.  It lists the components and stock numbers for each system.  It also shows two chargers that work well, the smaller charger is well suited to smaller & power capacity packs, the more expensive one also works with up to 6 cells.  This is intended to give folks flexibility to make their choice.

If you call the folks at Brodak and tell then you want a "10" size system, theis is the list they will use to fill it out.  Of course if you want to do a little mixing and matching you can do that too.