Since I have been lucky enough to live in apartments the last few years my Oscar has had to move a few times with me.
The trick I came up with and have been happy with is I have a Coleman camping cooler that I will put my 9 inch Oscar in. I only use the cooler for my fish so other items can't contaminate it. It has a hinged lid that is locked down by the handles to limit any spilling. Its large enough that he/she fits nicely and the water temp doesn't vary too much.
I remove all the items from the tank then use as much of the tank water as I can to try and lessen the stress on the fish.
Its small enough and light enough that I can pour him/her from he cooler to pre-setup tank. The last time I netted my oscar I got soaked from the splashing.