Ref the ducts & retracts, Kevin S scratch-built his ducts to fit, and also arranged his gear's legs to twist and retract. I've already posted pics on this forum somewhere, but should be able to rustle them up again from archives if you'd like a re-print
Ref the GP3300s, I'm with you. I don't know how long they'll last at 48A max and farless on average, but my 2x20-cell packs certainly work well, better output than 22 CP1700 to such an extent that the planes don't notice the extra weight.
Gonna get more GPs.