I'm thinking about taking my family of 5 (me, wife, 3, 2, and 1 year olds) on the road for 2 years, and I need to know what is the best diesel pusher I can/should get? We will travel to over 40 cities a year, and stay about one week in each city. We will live in it full time. Any advice would really help.
Maybe not the best (because that would be a Prevost conversion built exactly to your needs), but something pretty good that might work real well would be one of the two bedroom floorplans in Newmar's mid-engine Allstar line. These were designed specifically for families seeking sleeping privacy without sleeping in the living areas.
These were made for several years, at least through 2009. I don't know how many were made, nor how many were the two bedroom floorplan, because there were other uses (like toyhauler garage) of the extra volume available behind the rear axle. I just found a 2007 Allstar bunkhouse on RV Trader for $145,000. There could be 2008 and 2009 models languishing on dealer lots, 2-3 times that price.
I've seen motorcoach conversions with two or three bedrooms, but this is a whole different price category, 1.5 to upwards of 3-4 million for something this unusual, particularly if it means creating bedrooms below the deck.
Most manufacturers have a bunkhouse DP now and it's probably not a stretch to custom fit bunkbeds in a model that doesn't have bunks if the rest of the floorplan works better for you.
For fulltime living for 2 years, I'd want something that can sleep all three in their own bed and preferably something where there is a separate room and the best floorplan for that might be the Fleetwood Discovery 42A (It's only designed for 2 kids in the back but I don't think it's very difficult to modify the rear bedroom to have 3 beds back there (probably just have a bunk on the back wall instead of reclining bed)). The advantage of that floorplan is that it's also 1 1/2 bath and has an actual room for the kids as oppose to 'bunks in the hallway' like most class A bunkhouses.
I think Winnebago and Gulfstream also had bunkhouses where there was more of a 2nd room (there are probably others although the vast majority have the same layout as the Allegro with the bunks in opposite the bathroom).
The model refered to by tatest is the Newmar ATME3950 and ATME3951 and from what I've read, they only built about 30 or 40 from 2007 to 2009 so they are not easy to find. There was a forum member (Nathan Focht I think) that travelled with his family in one for a few years and they modified it to an extra bed - until fairly recently, his unit was actually for sale at some RV dealership). There was also a 2010 Newmar ATME4159 for one year but from what I've read, only 3 were built and there was very limited space in the loft area. I actually really like this floorplan (and would certainly consider it in the future for myself) although I've never seen it in person and I've heard complaints about having very limited storage space. I think they were about $240k new so that gives you an idea what to pay used. If you are interested in the 3950/3951, I think the 08 was bit better than the 07 (more power, possibly added the 'Comfort Drive' system (or something like that)).