Hi and welcome to the forums! :) Glad you are here and hope that you get some help with your question.
I have to say however, that I have never seen anyone post about the
Trailer Toad. I have seen some for 5th wheels but never one quite like that. There used to be a couple of manufactures that made much smaller ones but they have long gone out of business. It will be interesting to see if we have any members who have used one. It looks like quite an interesting device!
I noticed that the website has a pretty good FAQ section. You might want to ask your question there also.
I would take a guess and say that the only rating that would be affected would be the total weight rating (GCWR).
You would not have any tongue weight on the motorhome so you would have to be aware of your GCWR and any limitations on the total weight rating of the hitch you are using. I don't know if your frame modifications would have any bearing on the ratings or not.
Good luck with your question and I hope it gets some good response.
Barney