It is not the MH frame that is the limit, but the extension the MH manufacture adds to the end of the Chassis frame that is the limit. IF you look, it is probably made up of angle iron, flat bar, and sometimes, channel. This is engineered to support the part of the MH that is not mounted on the actual frame. This is why there are different tow weight limits, for the same chassis. You can reinforce the abomination the manufacture installed, but it will be hard to get a licensed mechanical engineer to sign off on it being up-graded for a heaver towing limit.