Your tune up should consist of replacing the following: Air filter, plugs/wires, fuel filter.
You should also inspect all belts and hoses, as well as all the fluids. (Power steering, tranny, oil, coolant, brake fluid)
As for accessing your rear plugs, you'll need the proper tools. A magnetic spark plug socket with a universal joint will work the best. Then you'll need a socket extension. Each plug may need a different length, depending on what's in the way.
And if something is in the way that's connected to the firewall, you can remove it, then reinstall when you're done.