People recommended Radical RC for replacement battery packs. I just ordered from them. (the price was excellent-have not yet received the packs) Give their site a looksee. As far as bubbles and sags in covering, I would recommend a heat gun as others have....use a gloved had to smooth down the covering as(after) you shrink it with the gun. ...and ya, watch the heat, a burn thru comes on quick! Good luck with the plane.
PS www.towerhobbies.com is always a fun place to look/shop for stuff.
PPS Braves drool,SOX RULE :^)