Lite weight Toy Hauler

go look at some horse trailers with living quarters. The living quarters come in small weekend packages to larger units. The back of the trailers can be just like cattle trailers and should be able to accomodate 2ea 4 wheelers

With a TH, 30ft isn't going to get you light or anywhere around 6klb dry. Need to look smaller 21-23ft to get in that kind of range. YOu can still fit 2 ATVs but will need a front kitchen model to do so.

Full size "sport" or "utility" ATVs?

Utility 800cc

My '21 is right at 6k without water/toys/groceries/fuel. It would fit 2 4-wheelers in line (or side by side if one of those is not a utility unit), or 1 SxS (like a normal Polaris 800, it might fit the 800S, the 900XP nope (too wide to clear the kitchen.

Mine is a front bed, side kitchen.

Look at the Rubicon 1905, 2500 or 2600. I have the 19' its about 5600 lbs dry and the 25'and 26' are about 7600 lbs. I have 2 full size utility quads that fit in my 1905 (inline). The other two will also accommodate 2 utility quads (inline). I think the 2500 has the best floor plan with a walk around bed.
http://www.dutchmen.com/rubicon/floorplans-and-pictures

If you don't need much extras, Living Lite VRV. I have a 8x22 which I fit both a Yamaha Viking 3 and a Grizzly 700. 7k fully loaded with extra fuel and full water. They do make a 5th wheel option now that I think is pretty light, maybe 7k?

Genesis supreme 19ss or 23SS under 6k. May not be for sale in your state. IDK. those floorplans are not uncommon.