According to the GM Upfitter guide, the 4500-6500 4x2 has a loaded frame height of about 29+ inches. This doesn't account for any cross member or bed floor thickness though.
The bed lift-in height of a 2020 3500 is around 39" unloaded- probably about 36" loaded. So, it sounds like the 4500 is close or even shorter depending on how thick your custom bed floor is.
A Host Yukon is 118" tall. So, that large camper on a 4500 would still be under or close to 13' tall in total. That doesn't seem too bad unless my math is off or I'm forgetting something.
sources:
GM Medium Duty Upfitter Guide2020 3500 Press ReleaseHost Yukon specs