We have a 2000 model M-18 and it was the best decision we made. Like you, we also upgraded from a tent trailer to this...a little more convenience, room, and still get to enjoy the outdoor feeling of sleeping out on the bunks. Ours has 2 queens (one in front and the dinette area makes into one) and a double in the back. So far, nobody has complained of sleeping in the back bunk area, even couples. It's easy to tow and fits in most of the places that our popup did. If we had to do it again, I think that we would probably try for the 21ss...that slide out is a really nice feature and gives a bit more room in it for walking around, especially for more than one at a time. The only issues we have had with ours (knock on wood) is replacing the hot water tank (got the electric/gas model with auto ignite) and replacing the 13" wheels and tires with 14". Good luck on finding your new rig!
Where we've been:
2000 Rockwood Roo M-18 Hybrid
2006 Dodge Ram 2500 Auto 5.9 Diesel
Gone but not forgotten -1986 Rockwood 1003 PUP