I drive a F250 8.3 ltr turbo diesel with a full size, slide on with shower etc. The tray on my Effie is 13ftx8 ft, it is very roomy inside & sits solidly on the tray of my Truck. The upside of this set up is that I can tow my boat & once you arrive there is nothing much to do to set up. The downside is it's height, as long as there are no low branches  or bridges it's not a problem. It is a little time consuming putting the camper on & off the tray. Otherwise I enjoy this set up, it suits me, although it wouldn't be any good for anyone with any problem climbing the steps to the camper. I have looked at a lot of slide on's & would agree most are like dog boxes inside, mine isn't. My camper weighs 900klg empty, so you would need a substantial vehicle to carry it once it's full.

My set up also gives me the opportunity to have a useful vehicle to use around my property when I'm not away. If it was a motor home it would just sit. I guess it's a case of "horses for courses"

Hi All Well I have now picked up my slide on and done the first trip. To date it has been exactly as I anticipated and I can definitely recommend this solution over both a fixed motorhome and a caravan for those with similar objectives to my own. ( Extended travelling sometimes with large boat attached and at other times back in the work a day world )
Unlike Peter above and perhaps like Honey Bunny I appreciate the ability to unmount my camper relatively easily and just use the base truck for other purposes. I have owned a 575 KNAUS motorhome and caravans and a camper trailer previously so at least I am not speaking as a one trick pony. I think attention to detail in the mounting systems and relative sizes can overcome some of the loading and unloading issues.
With a 4 step climb up to the floor level and another climb into the overcab queen sized bed it would not perhaps not suit the more mobility constrained amongst us. My fairly slight partner was however able to drive our small AWD truck for an extended distance on first outing, something impossible for her if we had gone with most other solutions.
We also intend to walk, camp, kayak and cycle in areas impossible to get anything but the most capable offroad camper trailer into and will demount the slide on at a base camp location and just drive the AWD truck into these areas.
Another big advantage was the ability to park just about anywhere (that didnt have a height constraint) like angled main street parking in country towns and just regular kerbside parking. Obviously not with boat in tow. LOL
After careful review however I think most one ton utes are too small to carry a really comfortable slide on along with lots of gear and retain any further genuine towing capacity.
Fold out slide on camper solutions are far more comfortable than most tents but share many features of these including the inability to just park up and see out the stormy night (or few days) in relative comfort.
As to Thunders original comments about slide on being top heavy cramped up mongrels, whilst agreeing our package is exceptionally tall at just under 3.7 meters clearance to the aircond, I have not found it overly top heavy to drive when mounted on our tiny AWD truck with dual rear wheels and it does have an excessive 2 meters of headroom ( due to the high overcab clearance required ), a queen bed, shower/toilet, 3 seat dinette and kitchen and it really isnt that cramped.
There are lots of negative comments on this forum about overweight caravans, towing issues and the like.
Alternatively the really big US trucks more suitable for substantial slide ons are both expensive to buy and run and perhaps some are difficult to get parts for in remote areas versus the extensive Isuzu network.
Our little car license AWD truck cost well under $60,000 brand new on road and can be found cheaper on occasions second-hand (they do seem to keep their value exceptionally well however). Combined with an often little used quality second-hand slide on or even new custom build it still works out as an effective package versus the cost of many similar alternatives I feel. Its perhaps not for those loving supreme comfort and extended stays in one place but it is a genuine alternative for those who like a constant change of scenery with a versatile range of uses.