Per CAT scales with current coach, we scaled out 2 different times to get accurate weights. 1st time was when we just left the dealer, so coach was empty. Advertised weights were: Dry 13420, Pin 2888, CCC 2532 and max GVW 16000. Had a '15 F350 sb, cc, 4x4 w/ 50 gal Transferflow tank. Truck's GVW was 11,500, rear axle of 7000 and tire of 7280. Truck alone = 8500. 5er alone 14,000. Pin = 2860. Truck + pin = 11460. Again, at this point = empty weights.
Once fully loaded and set for week vaykay, scaled our again (CAT scales). Truck rear axle = 7360 (+360#), Truck + pin (truck GVW) 12,240 (+ 740). Combined GVW = 24470. Take 24470 and subtract 8500 for truck = 15970 for 5er weight. At this point, I'm over on trucks GVW by 740# and slightly over on tires (80# no-one in cab of truck). Not too worried on trucks GVW or the tires.
As we were planning this years vayaky with FL being the bullseye, the truck tires were nagging me in pit of my stomach due to all the extra heat from air, road, extra weight and just plain going in circles. Ended up going the dually route in May. Like other posters, I too didn't want a dually but safety due to weight of things got the best of me and dually won out. Yes it's a pain at drive thrus or shopping lots and I do MISS my srw, but can say without a doubt, the dually was a smart decision for towing the Big Country. Still see many towing a heavy rig w/ a srw tho.
Bottom line is, plan on about 1500-2000lbs of "stuff" in the RV overall and ADD that to dry weights. Cannot tell you why we were so far off between published dry and real, but we were. My advice to OP is look for a RV that's under 15K max dry for a srw and you'll be fine.