jmal,
Welcome to JOF
With a 7,500lb GVWR TT I would be looking at a WDH rated at 1,200lbs.., IMO this will address the potential "loaded" tongue weight range of a TT in the 7,500lb GVWR class. One's desired "loaded" tongue weight will be 13% to 15% of the TT's gross loaded weight......, which is a variable of one's loading habits. Keep in mind that the loaded tongue weight is supported by the TV, so this weight is subtracted from the TV's "available" payload capacity.
I would assume that the Jayco TT you are looking at has the ball coupler mounted (welded) on the bottom of the TT's A-frame, you may find that a trunnion style WDH is better suited then a round bar WDH, in some applications the trunnion bar can provide increased ground clearance when properly adjusted.
I assume that your RV dealership is referring to the Reese Strait-Line WDH with integrated sway control, this is a great WDH. My Reese WDH Dual Cam (Strait-Line) has preformed great for over 10 years. Like any WDH proper sizing/adjustment is key for optimum performance.
Please keep in mind that published (brochures, web site, etc.) UVW's (dry weight) don't reflect the actual "as shipped" UVW, this may represent another 300lbs-600lbs depending on model configuration. Check the RV dealer's lot and refer to the yellow sticker on the side of the TT for the as-shipped UVW.
Just food for thought.
Bob
__________________
2016 GM 2500HD 6.0L/4.10
2018 Jay Flight 24RBS
2002 GM 2500HD 6.0L/4:10 (retired)
2005 Jayco Eagle 278FBS (retired)
1999 Jayco Eagle 246FB (retired)
Reese HP Dual Cam (Strait-Line)