If you read this site and others, you will soon realize that the suspension on these units is build for a compromise between heavy enough to handle the weight of the unit and soft enough to not shake the snot out of the interior.
To tow a boat or trailer you would be compromising the suspension without a doubt. Then you have problems with collapsed spring and bent axles.
I wouldn't dream of towing anything much heavier that a bike rack unless you are able and willing to do some beefing up of the suspension.