The ability to tow will depend upon your specific chassis and the hitch rating. My previous W20 chassis had a GVW of 20,700 and a GCVW of 26,000. If I loaded the coach up to full load that would allow me 5,300 lbs. However the hitch was only rated at 5,000.
On a W22 the GVW is 22,000 while the GCVW remains at 26,000. If you load up a W22 to max you will only have 4,000 left for the toad, also with a 5,000 hitch. If you reduce the load by 1,000 lbs you could safely pull a 5,000 lb toad.
On my Bus I have a 32,000 GVW and a 42,000 GCVW and my hitch is a 10,000 lb hitch. The 400 ISL has plenty of power so towing a heavy toad on a DP with these specs is not a problem. But, not all DPs are the same so you need to check these 3 numbers to determine if you can safely haul a heavy toad. Some units have a 10K spread between the GVW and GCVW but the hitch is only rated at 3500 lbs so you have to check carefully.
Mark & Leann Quasius
2016 Cornerstone 45A
2007 Allegro Bus 42QRP (Sold)
2012 Jeep Wrangler Unlimited - Rubicon