This may be what you could use as an alternator/generator
onboard charging system:
http://www3.towerhobbies.com/cgi-bin...?&I=LXFV20&P=0

The firewall bulkhead would have to be a minimum of 1/4" thick aircraft
birch 5-ply plywood for an IC engine, braced accordingly in the fuselage.

Is the engine you intend to put in the plane a YS-FZ140 4 stroke model engine?
If so you are going to need an awful lot of fuel to keep this thing airborne for
12 hours, non-stop. Fuel for a 140 4 stroke motor= 12 hrs x 60 min= 900 min.
900 min. x 1.25 oz per min ( estimated)= 1125 oz. divided by 128oz (1 gallon)=8.8 gal fuel.
8.8 gal fuel x 7.7 lbs per gallon=67.76 lbs of fuel.........
plane weight at 40.1 lbs + fuel weight 67.76 lbs= 107.86 lbs gross weight.........
and it gets more improbable as the equation goes on, as I don't think the airframe
could store or carry that big a volume of fuel..........