With this little bit of additional information, I would do the following:
(a) find a good welding shop;
(b) have them add two hitch receiver tubes of 2 1/2" square 1/4" wall tubing
(c) fabricate a nice aluminum platform to load the bike onto with a ramp (aluminum will cut the weight by half);
(d) load the bike and go.
If the owners manual for your coach indicated what the tongue weight of a trailer being pulled by the coach is WITHOUT weight distribution equipment will be close to the carrier and the bike, I think you have a winner.
If your owners manual gives you a tongue WITH weight distibution and it is more than your carrier and bike, I still think you have a winner as you have spread the weight out over the two or three receiver tubes you have added to your hitch.
Now, lets get some decent weather, load those bikes, and head out on a new adventure!!!