Not wanting to hijack the thread, but would like to add to snokings comments. We had a '03 F250 PSD,cc,4x4,sb, 50 gallon T-flow tank and rated for 8600 GVW. Max 5er weight was 10,000 and max combo wt was 20,000. Weighed on a CAT scale, she came in at 8500 lbs by ITSELF!. With 5er, fully loaded, trucked weighed 10,500 and combo of 21,500. If I recall right, it was near capacity on rear axle, below front, but over on gross. Tho truck towed it just fine, had to be in mindset of leaving a gap between me and person in front.
This being said, we got rid of the '03 and now have a '15 F350 PSD, CC, SB, 4x4, SRW, 50 gallon T-flow tank and she weighs the same as the '03 did within a few lbs. GVW is 11,500, max 5er weight is 15,700 and combo is 22-23,000. Will be getting a BC 3560SS which will pretty much max out the 350 in SRW form. By my early rough calculations, will be over one the ratings between 500-1500 lbs (could be wrong). Like snoking said, I too don't condone towing overloaded. 1,000 lbs is 1,000 lbs,but shouldn't kill the truck. If 3-5000, that's a different story. It's your call, but just keep in mind leaving a gap all the time which someone will always fill.
A friend of mine years ago told me that all mfr's test their trucks with weight far more than we will ever carry to find their breaking points (probly twice that of what they tell us we can tow safely). All this to CTA (cover their *****). Also, in regards to the Ford line, back in early 2000's, their 350's were rated at 9,900 and folks towing 15-16K w/ them. Don't recall a lot of fuss then. Now the 250's have a GVW of 10K and 350's (SRW's) 11,500. With sue happy atty's nowadays, we have to COA (cover our *****). All RV mfr's are guilty of making heavier and heavier coaches which forces us to have to go to 350's/450's or DRW's. Yes I towed w/ our '03 for 11 years w/o a problem, but always on guard while doing so. IMO, 250's should tow <14k RV and pin of 1800-2500 MAX.