Sabre will void your warranty. Though on a 2013, it's already void.
The only anecdotal advice is that there was 1 user on the ForestRiverForums.com with a 36QBOK who added an Idaho Tote type of "trailer" for a gulf cart. A bit later, he ended up with a buckled frame between the two axles. I know that Sabre denied him due to that. I don't think anyone can say it was definitely it, but I've seen enough that I wouldn't do it.
If I get a golf cart, it's going on a specialty-built rack on top of the truck's cab. The golf cart will have a removable top that will come off for travel to limit the golf cart's height to be no higher than the fifth wheel itself.