I'm with the crowd on this one.
Other than the obvious serious issues with this concept;
- a 5 to 6 ton single axle trailer with no ability to balance the load or adjust the axle position would be brutal to tow,
- if you leave the original axle, the gears & axle will add tremendous drag and making hydraulic brakes work will be a whole other challenge,
- it would require some serious engineering and a highly-skilled welder (dissimilar metals of unequal thickness) to fabricate something safe & legal,
- a truck big enough to safely drag this down the road would easily cost the price of a good used Motorhome itselff.
Given all of the above, I'd have to say if you don't want a motorhome, buying a decent used travel trailer would be your cheapest option.