1700# est for the iForce Hybrid. I don’t think official numbers are out. Battery weight will be an interesting addition and impact.
It will be under 1,000lb in reality... probably.
I'd suggest making the camper 80" wide external at most. Keep any gaps small. Also, facets are good.
The Aterra camper is a good example of doing flat panels "right". If you want to make a full camper for a midsize, I think it's important to maximize space utilization, be at least 72" high inside, and be aero, and minimize frontal area.
Another option vs Aterra style, would be a molded nose to go on the front. That would be best for aero.
I've always 'assumed ' the manufactur use of 'max payload ' was used
for safety, like stopping, cornering, excessive wear..et al
I could be wrong though.
It's the manufacturer warranty and liability limit, based on the stock vehicle. If you are over GVWR and something fails, they can deny warranty on that basis. If you are over GVWR and are in an accident, Toyota isn't liable.
If you do proper upgrades on suspension and tires, then safety isn't a concern within reason. Excessive wear? No doubt a Tacoma hauling 2,500 lbs is going to have a harder life than one that isn't!... but that amount of weight isn't unusual, either.