At least through 2004, motorhomes built on the Express 3500 cutaway chassis usually got a 3500 pound tow rating, and had a 12,300 GVWR (though smaller ratings were available).
Later Workhorse versions with GVWR higher than 12,300 pounds may have gotten higher tow ratings.
Door plate will have the GVWR and front and rear axle ratings. Carrying capacity will depend on how much is the actual weight of that model motorhome.
Tom Test
Itasca Spirit 29B