RVs don't follow the same 'rules' that you are assuming they should, as cars may have to, since they don't fall under the same regulations. But, your freightliner chassis is certainly 'protecting' you, though you may assume that just because a 'bumper'(old school) is not evident, you don't have any - you are sitting way above any contact with any 'bumper' you may have, so 'safety' may not be actually what you are referring to - damage to your generator may be.
I would say though, that there is also plenty of 'room' before the generator would be impacted, unless a high impact, in which case it's certain that damage would occur anyway.
I don't know that a 'bumper' is really any answer - if you don't follow too closely and maintain your brakes, you'll be 'safer' than most anything a vehicle manufacturer can give you, especially since most accidents are front-end damage by a vehicle not stopping in time.
The frame rails of the chassis extends quite well into the front-end cavity, and are actually already providing protection.
two Campers, two Electric cars
former diesel pusher traveler