Let's start with your RequirementsStatement.
How is your experience operating a forty-foot vehicle?
In my case, an all-steel vehicle offers more resilience than a plastic exterior... because I tend toward bashing through rather than doing a ballet around.
Why were you considering a forty instead of a thirty or twenty?
For those remote mountain lakes and isolated Baja beaches we prefer, our short wheel-base ground-clearance makes more sense than would high-centering during ground-breaking.
Where will you travel?
Engine torque on the 5.9 is great in Dodge pick-up trucks; what is your performance prediction in the forty FOR YOUR USE?
Our Cummins 505ci is nicely adequate for our 14,000# across the scale... but we putter along in the slow-lane at 52mph during two-hour driving days.
After installing insulation plus flooring/ceiling, how 'hunchy' is the interior?
How far are you going with a conversion?
2003, we converted a 1996 Ford CF8000 commercial truck to our concept of an ExpeditionVehicle.
Our interior is three paces across by seven paces long... perfect for three RedHeelers and two adults (plus a frequent yummy third).
We acquired the truck after my Very Significant Other got sick.
We completed our conversion -- while selling everything -- less than a week after diagnosis.
I think your potential purchase was probably engineered for short slow city-routes.
If you intend to use it as-engineered, it could be a great foundation FOR YOUR USE.
For our use, the exterior would quickly resemble a demolition-derby survivor.
Not that this would be a bad thing, but I imagine it would tend to give pause during introductions on first-dates.