Well, #1 You could use some 2x2's build a frame and then cover it with plywood. Then secure this to the floor and attach your dinette to that. But, it would cut out room and look ugly. You maybe could cover it with paneling.
What I'm trying to say since I don't explain my self very well is to build second a mini wall from the floor up to the bottom of the window. Sorry if you don't understand me.
#2 Maybe you could remove the paneling from inside the TT and then add support behind it then replace the paneling???
I sure wish I could make one of these work in my TT. Taking the two table supports out and then putting them back the next morning while lining everything back up is a pain in the you know what.