I'm just going to throw in my .02 cents here. I have a Dodge Dakota with a 4.7L V8, aftermarket coil over shocks, and a tow rating of 7000lbs. I currently tow a 20' trailer that weights 5000 when it is loaded (3500LBS Dry)
I can tell that I feel that 5K is max for my truck and I wouldn't ever consider a 29' trailer with the tow rating of 7K that I have. Also does your truck have a tow package and a transmission cooler, if it doesn't have a transmission cooler you better get one before you start towing anything, they aren't that expensive and well worth the investment.
The dealer will sell you the moon and tell you that it is towable with your current truck but that's not always the case, like others have said be careful and take your time. Don't let the RV dealer tell you what you can tow and talk to your truck dealer first for a realistic estimate.