If the Chieftain already tends to run hot you may need to address that first before adding a load to it. You may need to go through the cooling system and the transmission first to ensure the antique drive train in the Chieftain is up to the task. Transmission band adjustment, new filter and a larger transmission cooler may be required on those older motor homes before loading them up with toads, etc. Also consider adding a Water Wetter or Lucas Super Coolant additive to the cooling system after a good cooling system flush using a 50/50 blend of white vinegar and distilled water.
A thorough inspection of the rear frames that the hitch is attached too is also in order since many times those are mounted to extensions of the rear frame and not the P30 truck chassis and are mild steel that rots more easily than the truck chassis does.
2001 Winnebago Adventurer WFG35U