Pop-up Camper roof rack/Luggage rack capacity

I have been doing some research looking on some pop-up sites and they claim that coleman pop-up roof closed has a 300lb capacity and when up and 150lb capacity. So people are putting racks on them for Kayaks and bikes. So I am wondering if a kart that weighs 150lbs would be a viable option if I  put it on a rack? I have seen cars with a rack and a kart on top, but I would imagine that capacity is much higher for metal. I am looking at used Pop-campers, but almost impossible to test this theory without purchasing one.

In reply to trigun7469 :

It sounds like it would work as long as the kart is off before the top goes up & vice-versa. 

What do the clamps look like and how are they held to the roof ?

Years ago I had a VW bug which had a roof rack mounted to the rain gutter , it had  2  tubing pieces , front and back in the groove and one clamp , this was each side , 

We put a transmission on the rack and  the weight pushed down the tubes and made the clamps loose, 

So make sure the hold down clamps stay tight with whatever weight you put on it and check it often !

Which roof does it have?  Some had metal roofs, and some had plastic.  Is it just going to rest on the roof?  I made a bike rack for ours that had a plywood bottom to spread the load and never had any issues with it.  

There is a really wide range of capacities in popup camper roofs, especially on the older ones.  The roof structure matters, but so does the lifting mechanism. 
 

I have a friend who added an AC unit to the roof of a camper that didn't come with one, and it collapsed the roof and totaled the camper with his 6 kids inside. 
 

I would not have a big issue with it in the down position, but I'd never raise it with a kart on top. 
 

An inability to raise the roof at the roadside really limits the functionality of a popup. 

Here are some examples on cars, I am checking to see how people are securing them.

Car roofs are attached, and designed for rollover protection. 
 

Popup camper roofs are held up by spindly extending poles with no diagonal bracing. 

In reply to SVreX (Forum Supporter) :

That's why I am wondering if I would need to make a frame underneath the roof to stiffen it.

In reply to trigun7469 :

I don't think it would help. It might make it worse. 
 

The weakest link is the telescoping legs, not the roof platform. Adding weight to the top adds stress to the legs, and there is no way to add diagonal bracing.  
 

If you add stiffening to the roof platform, you just add more weight. 
 

When a popup camper roof collapses, the roof platform doesn't fail. The legs do. The roof platform rotates and all 4 legs twist like pretzels until the roof platform is on the ground (in one piece).

So my opinion is, no you can't add weight to a popup camper roof beyond what it was originally rated for (and some of them are designed to handle cargo weight). 
 

If you will NEVER lift the roof with the load on top, I think you would be fine (probably with no reinforcement). But if there is ANY chance you might sometime try to raise the roof (even part way) with the load on top, then I say no.