If the "cruiserlift" is to be used to carry a cruiser (thinking Goldwing or one of the bigger Harleys) I don't think you have enough frame/coach to support that kind of weight.
I have a similar coach, and though theoretically it has the gross to do what you want - that weight is going to be in back of the motorhome, creating some incredible leverage on the rear axles. Even though the axles are rated for it, with the bike lift to axle distance involved, I have some pretty serious doubts about the frame's capability to handle it. TO add to that concern, I'm guessing there's a pretty good reason the hitch is only rated for 300 lb of tongue weight.
I'd say no way, but I'm not the one wanting to take a bike with me...
1997 37' HR Endeavor, 275hp Cat, Freightliner
03 CR-V Blue Ox, Ready Brake