You could get an Autohaven 4x4 tent as these allow you to reverse the vehicle inside the tent or leave it free standing. I have one and they are brilliant.
ive made a roll out canvas one on the near side too.
Im making my rear out of normal green tarp, jubilee clipped to my rack (tubular type).when rolled up I keep it in place with rubber tree stake ties from b&q. I was goin to have extendable pole sliding out the back of the rack but looks unstable! so im using 2 extendable tent pole uprights as with my side awning & guy roping them. Bit more of an effort to put up but for £40 who's complaining?!!