I have heard that you are better off using a carboy over a bucket for secondary fermentation because buckets are more prone to leaking air, which isn't near as big a problem when your beer is pushing off a lot of CO2 (because CO2 is going out, so air isn't coming in) but may be an issue when your beer is putzing around in a secondary fermentation bucket for three weeks.
If you have kegs and the beer is in secondary I'd just keg it and jack to 30psi to hold the lid and then you can just chuck your kegs in the trunk and roll out.
