Winfried
Doesn't it concern you that there will be a lot of weight in the belly of the plane. That IMO would affect knife edge, rolling manuvers, and also verticals.
I found this out flying alot of foamies. As example if you were hovering a plane and had alot of weight in the belly it would want to fall out and would require up elevator to sustain a vertical hover.
I also feel that having to turn the plane over to remove batteries would be uneasy. Although, I don't believe you have a removable canopy. Not sure about the oxalys. If I switch to the 3700's at some point I may have to go in through the chin cowl.
I would be curious to see how it affects flight.
Just giving you something to think about.

Nice plane!!!
Chris