Depending on how much "older" and whether Ford, Chevy, Workhorse, VW, Daimler or Dodge, and which level in the chassis series, it could be as little as 2500 pounds or something in excess of 5000 pounds, for the chassis itself. A motorhome manufacturer might further limit towing capacity based on frame extensions and towing equipment installed.
New series E-450 have GCWR of 22,000 pounds with 6.8 V-10, implying tow capacity of 7500 when loaded to 14,500 GVWR. Ford says 10,000 max tow, but that would have to be a relatively light MH on the chassis. E-450 with 5.4 V-8 is GCWR 14,000, but it is unlikely that you will find that combo in a C motorhome. A couple manufacturers used the bare chassis E-450 with 5.4 to build "RUV" Class A's for a while, but I think most went on to use the V-10 or moved to other platforms.
Older E-450 had GCWR of 20,000 pounds implying tow capacity of almost 6000 when loaded to GVWR of 14,050. Again, Ford rated the chassis at 10,000 max tow, applicable for vehicles lighter than a typical motorhome (chassis itself is around 5000 pounds, depending on equipment package).
On earlier E-450 some RV manufacturers installed 3500 pound hitch limiting tow to 3500. Others installed 5000 pound hitch, rating to 5000 flat tow, 3500 load carrying with typical max 350 tongue weight, this because the frame may be extended 6-10 feet, changing leverage at the hitch.
E-350 cutaway chassis is currently 18,000 GCWR with the 6.8 V-10, 13,000 GCWR with the 5.4 V-8. It has been 17,700 GCWR with the V-10 in the past, before brake and suspension upgrades somewhere around 2008 model year.
It was once conventional for the Express 3500 cutaway to be rated GCWR ~ GVWR + 3500, so usually about 16,000 pounds when used at maximum GVWR of the era, 12,300 pounds. Workhorse upgraded from this to get GVWR 14,050 and GCWR 18,000 but still labeled it 3500. When GM came back into the market they produced an Express 4500 matching E-450 capacities. But that's recent, so if an older Express 3500, towing capacity is usually 3500, equipment installed to be consistent with Chevy's limit at full weight.
Older G-30 or Dodge B-300, expect no more than 3500 pounds, and that's going to also depend on which engine is installed: 350 vs 454 on older Chevys, 318 vs 360 vs 440 for Dodge B-series.
Other platforms, I think the VW T4 used by Winnebago was limited to 1500 pound tow, Sprinters are going to be around 3500-4000 at the most, might be substantially less depending on model year and engine used.
Plan for a 3500 pound flat tow, and you'll be OK for most.
GVWR and axle and tire ratings will be in the DOT mandated label in the door jamb. DOT does not put GCWR on this label, it will be in the owners manual. RV manufacturers will a supplemental label with VIN and ratings for finished vehicle, which might or might not include GCWR. I had to go into my owner's manual from Winnebago to get finished vehicle tow ratings, which matched a label on the hitch receiver.
Tom Test
Itasca Spirit 29B
