I've got an Asgard tent from the Boy Scouts. 4 season octagon shaped and fits three adults snug so two is easy. Packs perfectly into the 40 ltr side, using a compression bag, with room for a self-inflatable mattress and rods.
The best purchase to go with any tent is a compression bag. I bought a bunch of compression bags in the off season and the gear I packed last summer that required a 50 ltr top bag in the passenger seat is no longer required.
2nd best purchases are stuff that minimizes gear and amounts of gear. Stuff pocket sized stoves, mini headlamps, self dry shirts, shorts etc.
I spent about $50 on this stuff and saved myself buying a top box.