I'm not an RC guy, but my friend, Nacho was, right up until his sudden passing early this year.
Since then, my wyfe and I have been helping his widow and kids to sell off his vehicles, boat, motorcycles and 30 years' worth of RC planes, cars, buggies, boats, engines, parts, batteries, radios, etc. I have posted up the bulk of the large scale planes in new, semi-new, decent, and rebuildable condition in the forum's Classified section, and have just sold one of the larger planes, a Great Planes Revolver which has an approx. 55" fuselage length, 28" tail width, and 14" tail height; my plan is to build a box with 2-4" additional on each side.
I'm starting with a selection of large empty boxes sourced from a nearby auto body shop; these are available every day of the week for free, and also typically include a variety of packing and stuffing materials. Total cost so far = $0.00.
Next, lay out the closest oversize box...
Looks like the nose is too long, so I'll remove the spinner & prop...
Had to remove the motor, too; the shaft was still too long.