Some of that is going to depend on which model you have, which WD system you are using (especially the rating of your spring bars), and what your tow vehicle you have. And, which cargo box you use.
I would be mostly concerned about the older Sunlines that have 5" C-channel for their A-frames. They can take some additional weight, but it would be difficult to guess when some becomes too much.
If your WD spring bars are already at their limit, it may be a factor. Worst case would be swapping up to the next size bars.
Your TV's rear axle rating may be a factor especially if you are already close to the max. before adding the cargo box.
Pat (emam) installed very long and heavy battery holders behind his propane tanks to accomodate 4 golf car batteries. And, he has a custom bicycle rack above the propane tanks. Keep in mind he has a newer 2499 with the much taller frame and A-frame material, a 3/4 ton TV, Air Ride leveling system, AND the weight on the A-frame is offset by the motorcycle they carry on an extension on the rear of the TT.
If you have followed his adventures, he found significant damage to the TT's framing where the axles are connected to the main frame. It was a straightforward repair, but not cheap. How much of that damage is attributable to the added weight of his unit is hard to say given the mileage and variety of on and off-road terrain that they have covered.
A great number of us have some additional weight on the A-frame. I have a second battery box full of steel parts for my FCP Lean-To. It weighs at least as much as a second battery which many, many folks have. I would not hesitate to add another hundred pounds or so to my A-frame.
One final thing to consider, if you have a 2499, there were a couple of years that had serious issues regarding the A-frame connection to the main frame.
'12 F250 4x4 Super Duty PowerStroke 6.7 diesel
2011 to present: '11 Cougar 326MKS
1999 to 2011: '99 Sunline T-2453
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